Dog training is an area where emotions run hot, and you will hear many strong opinions or judgments from just about anyone and everyone. The key to weathering the tempest is not to be overly influenced by any one source. Gather information on the various training methods, and then judge for yourself which best suits you and your dog. Be careful not to be fooled by some of the jargon that people use to describe some of the techniques, e.g. leash "correction" = leash jerk. Also be careful not to accept a single person's opinion as truth (even if the person is supposedly a professional trainer or behaviorist). There is no body that governs who can be called "trainer" so examine resumes carefully. Even if a trainer appears experienced, do not take what he tells you as gospel. There are many experienced trainers out there that have strong biases towards techniques that may not be appropriate for your dog, and/or may not create the type of relationship you want.

A common epithet to look out for is "Technique X will never work for your dog". This is sometimes combined with "because he is dominant/stubborn/fearful/aggressive". Simplistic statements like these are never true. Research the technique and/or try it out, then form your own opinion. Another favorite is "Technique X does not cause any pain/discomfort". This is sometimes combined with "it is just to get your dog's attention / get your dog to calm down". Decide for yourself if it actually causes pain or stress, don't just take one person's word for it. For example, to test if a leash jerk causes pain you could try the collar on yourself (on your leg) and do a gentle leash jerk, or for a more painless experience get information from a variety of sources on the web. Below I try to provide a general overview of dog training techniques including their pros and cons. It is up to you to decide which is best for you and your best friend.

There are two classes of training techniques, reward based (give/remove something that your dog likes) and aversive based (give/remove something that your dog dislikes). 

In reward based techniques, you first identify what your dog likes. You then encourage or discourage various behaviors by granting or taking away access to these rewards. For example if he sits, he gets a food treat; if he is calm he gets to interact with other dogs; you stop him from chewing on your shoes by redirecting him to a Kong toy. Which rewards work best for your dog depends on his personality and to some extent on his breed (i.e. whether they are hunting dogs, herding dogs, tracking dogs, etc.). It is generally not too difficult to observe what your dog loves to do and identify a reward system to which he will respond. Almost all dogs will work for food ^.^ Reward based techniques are also commonly referred to as positive reinforcement techniques. These more scientific terms, however, may get somewhat confusing because taking away a reward is referred to as negative punishment. For simplicity, I use reward techniques to refer to both.

One common misconception is that you will not be an effective leader of the pack if you use a purely reward based system. Sometimes this is combined with "especially if your dog is a Chow, Shiba, etc." This is not true. Dogs like Chows and Shibas tend to be independent, stubborn, and are not as easy to train as most other breeds but they can definitely be trained using a reward based system. Jean Donaldson, who is a strong proponent of reward based techniques, owns Chows, and you can read about how she trains them in her book Culture Clash.

Suzanne Clothier writes a beautiful book on why you would want to cultivate a reward based relationship with your dog. I highly recommend Bones Would Rain From the Sky. The first chapter is a bit over the top, but the rest of the book is very moving. Don't Shoot the Dog by Karen Pryor and The Other End of the Leash by Patricia McConnell are both very good books that describe how you can train your dog using a reward based system. Ian Dunbar is also very well known for his work in this area.

Advantages

• Little danger of losing trust 
  One of the biggest advantage of reward based techniques is that there is little danger of losing your dog's trust even if you mess up your training. If you don't do dog training as a living, chances are you may not always execute your training methods perfectly or even close to perfectly. Many of us will make many mistakes before we improve. If you are using a reward based system, a mistake may get your dog a bit confused as to why he is getting a reward. A string of continuous mistakes may inadvertently encourage unwanted behaviors such as jumping but that's about as bad as it gets. Aversive techniques, on the other hand, can very easily cause loss of trust and may encourage aggression when not implemented correctly. 
• Mistakes will not damage your dog either physically or mentally
  The worst that happens to your dog is that he doesn't get access to the reward. He may look at you cross eyed but he won't go home with a hurt trachea or other bodily harm that can happen when certain aversive techniques are not implemented properly. Note that prolonged use of choke collars may cause harm to your dog even when the collar is fitted properly. The following excerpt taken from 8 Paws Up - Lab Training - Prong Collars and Prong Collar Info has the following shocking results.

Study of Prong Collars in Germany (Information about study taken from an Anne Marie Silverton Seminar)

• 100 dogs were in the study. 50 used choke and 50 used prong.The dogs were studied for their entire lives. As dogs died, autopsies were performed.
• Of the 50 that had chokes, 48 had injuries to the neck, trachea, or back. 2 of those were determined to be genetic. The other 46 were caused by trauma.
• Of the 50 that had prongs, 2 had injuries in the neck area, 1 was determined to be genetic. 1 was caused by trauma.

• Helps create a dog that is happy and eager to work
  When you use a purely reward based system, your dog will be more eager to work because work time means reward time. Aversive techniques, on the other hand, may decrease your dog's interest in working. He may decide that lying around and sleeping is much safer and less stressful than going for a walk or working where he may be "corrected" for making mistakes.

Disadvantages

• Your dog may not always follow commands and may take longer to respond
  For most dogs, a reward may not be as strong a motivator as an aversive stimulus (e.g. leash jerk, slap on the muzzle, alpha roll). Some dogs may dislike an aversive stimulus to such an extent that they fear it. Fear is one of the strongest motivators for dogs and most dogs will respond more consistently and more promptly to it compared to a reward. Consistent and prompt response to commands becomes important when your dog is involved in a life or death situation e.g. running into traffic. 
  
  
• May need to get creative and come up with your own techniques
  Reward based techniques may sometimes require a fair amount of creativity in trying to out-think your dog. This is especially true when you are trying to stop bad behaviors such as jumping, leash biting, mouthing, etc. While there are many reward techniques for stopping these behaviors, they may not always work with your dog. I.e. your dog may decide that the reward from the bad behavior outweighs your reward. You may need to concoct and try out a variety of methods and reward systems before finding one that works well. In contrast, the same aversive technique (e.g. leash jerk) can be applied to a wide variety of situations. 
  
  
• May need to carry rewards with you when on walks and outings
  Note that dogs do not care about the monetary cost of a reward and some find "rewards" such as sticks, pine cones, and leaves to be quite awesome. If you find yourself in a situation where you need a quick reward, some may be readily available in the trees and bushes around you. It is sometimes possible and very desirable to use other dogs and people you meet during outings as rewards for your dog. For example, if he doesn't jump, he gets to go up and meet the new person. Once he starts jumping move him back, do a sit, and restart the greeting. As your training progresses, you can begin to phase out food rewards. Be careful to phase the rewards out slowly so that your dog stays motivated.
  
  
• Your dog may gain weight from excessive use of food treats
  Obesity can sometimes become a problem if you give your dog too many treats. This issue can be easily resolved by using his meals as training rewards, using smaller sized treats, and switching to low calorie food and treats.

I divide aversive based techniques into three classes: pain based (e.g. leash correction, muzzle slaps, ear pinch, electronic collar); dominance based (e.g. alpha rolls); and other which may include making loud noises (e.g. shaking or dropping a can of pennies, loud horn, clashing pots), using unpleasant smells (e.g. spraying bitter apple on furniture, spraying diluted vinegar or citronella on muzzle), using unpleasant sensations (spraying water on muzzle, dumping water on body) or anything else that your dog dislikes. Different aversive techniques may place more or less stress on your dog. In general the pain and dominance based techniques are more stressful.

With aversive techniques, you encourage or discourage behaviors by applying (positive punishment) or stopping (negative reinforcement) an unpleasant stimulus. For example, if your dog breaks from his stay before you release him, you give him a leash jerk; if he starts biting on the leash, you give him a leash jerk or spray water on his muzzle; if he jumps, you give him a leash jerk or knee him. We quickly see that unlike reward based techniques, a single aversive technique (leash jerk) can be used to both encourage and discourage a wide variety of behaviors. This is possible because pain is a strong motivator and will be effective in many situations. It may therefore seem that aversive training is a lot simpler and easier to execute than reward based training, but that is not really the case. 

Executing certain aversive techniques, such as the leash jerk, can be very tricky. First of all it must be a jerk and not a tug, or it will not be effective. When I first learnt this technique, I was almost always tugging, and tugs do not deliver a force strong or quick enough to produce an aversive response. Secondly, it is difficult to deliver the jerk with the proper amount of force. Most beginners will tend to deliver leash jerks that are too weak. This causes your dog to become habituated to the little jerks so that it no longer has any effect other than a slight annoyance or irritation. To avoid this, some training literature suggests providing a few stronger corrections with a "No" command at the beginning. Afterwards, your dog should just respond to your "No" command or light jerks because he knows that you can and will apply the stronger jerk if need be. However, if you deliver a force that is too strong at the outset, you may cause your dog to break down, especially if he is a shy or sensitive dog. Getting a good trainer to show you how, when, and where to apply these techniques is extremely important.

Cesar Milan, one of the most popular and well known dog experts, uses mostly aversive based techniques. He has a popular TV series called The Dog Whisperer  on the National Geographic Channel. His book, Cesar's Way, has a very engaging writing style and Cesar has a fascinating story to tell. One of the things you notice first about Cesar is his great confidence and natural talent in being able to read dogs. This is very important when applying aversive techniques, because if these techniques are not implemented properly, they may cause physical and mental harm. 

There are a variety of other trainers that use both reward and aversive based techniques. The Monks of New Skete are well known for their dog training program, and their book How to be Your Dog's Best Friend is an excellent, well-rounded book on how to take care of your dog. This book has a lot of useful information on what to feed your dog, where you should let your dog sleep, grooming your dog, and many other day to day questions you will have in raising your canine friend. The Monks use a combination of leash jerks, praise, and food treats.

Victoria Stillwell, a well known dog expert in the U.K. hosts a very interesting TV series called Its Me or the Dog on Animal Planet. Victoria uses mostly reward based techniques. Sometimes, she will borrow a few techniques from the aversive area that are not pain or dominance based. In this way she has access to a wider variety of techniques without ever placing too much stress on the dogs. 

Advantages

• May get more consistent and prompt responses to commands
  As with any animal, dogs are very sensitive to danger (threats), as this is crucial to their survival in the wild. When faced with a stressful stimulus (e.g. pain or a dominance threat), dogs will most likely try to resolve the stress quickly and return to a safe, comfortable, state. Many dogs will perform a sit, down, stay, etc. consistently and quickly because they do not wish to face the stress of an aversive stimulus. Once you get consistent and prompt responses from your dog, you can give him more freedom and let him participate in a wider range of activities. A very obedient dog can walk off leash, go with you everywhere, etc. Many aversive based trainers point out that a good command response is crucial when you are yelling "stop" and your dog is running into traffic.
  
  
• May get responses to commands in a shorter period of time
  As described above, dogs can be very motivated to avoid an aversive stimulus. You will probably start to see results to simple commands in a shorter period of time compared to reward based techniques. In fact, your dog will probably respond best in the initial training sessions. Performance may degrade later once your dog gets used to (habituated to) the aversive stimulus.
  
  
• Do not need to carry around rewards such as treats or toys
  You always have what you need with you. 

Disadvantages

• May cause loss of trust
  The most important danger of using aversive techniques is losing your dog's trust. Care must be taken not to over-correct your dog. Try to set him up for success and reduce the chances of him making mistakes. If you are seen as the source of unpleasant things, your dog will lose trust in you and may start avoiding you. The trick of implementing aversive techniques is to make it seem like the source of unpleasantness is not coming from you, but is rather a result of your dog's actions. Spraying bitter apple on furniture is an effective and safe aversive technique because the dog does not associate the smelly furniture with you. Rather, he discovers on his own, that these particular pieces of wood and stuffing are unpleasant so it is best to avoid them. It is important to follow up an aversive correction with praise and rewards once your dog complies with your command. This shows him you are also the source of happy praise and good things. It is also crucial to time your aversive correction and subsequent praise accurately, so that your dog does not get confused and frustrated because he is unsure what the aversive stimulus is for and how he can make it go away. 
  
  
• May encourage aggression and other unwanted side effects
  There are four ways a dog can deal with the stress of an aversive stimulus: fight, flight, freeze, or appease. Depending on the temperament of your dog and his level of trust and respect for you, he may choose to fight or flee rather than follow your command (appease). You can probably correct this by refining your aversive technique (i.e. ensure appropriate level of force, no over corrections, redirect source of correction away from yourself, etc.). If your dog continuously chooses to fight, then you are encouraging aggression in him, and he may ultimately become a dangerous dog. If your dog continuously chooses to flight then you may break his spirit and he may become a fearful and unstable dog. If you are not careful, your dog may also associate the aversive stimulus to the environment or other objects in the environment. For example, if a leash jerk is always applied whenever he sees another dog, he may associate the pain with the other dog rather than to his lunging and jumping actions. As a result he may become aggressive or fearful towards other dogs. In this same way, your dog may become aggressive towards your spray bottle because he sees it as a source of unpleasantness. Make sure the bottle is hidden as much as possible before, during, and after the correction.
  
  
• Some techniques may injure your dog if not implemented correctly
  When you are using a training collar such as a choke chain, prong collar, or martingale collar, make sure you consult a trainer on how to fit it and use it properly. The choke chain, especially, is not recommended as it can cause harm with extended use, even when fitted properly (refer to Study on Prong collars above). Use of all pain and dominance-based aversive techniques are best done under the direction of a trained professional. Incorrect implementation of some of these techniques may cause physical harm to your dog, as well as physical harm to you and others if your dog becomes aggressive.
  
  
• Response to commands may degrade once your dog gets habituated to the aversive stimulus
  If you overuse an aversive technique, it is very probable that your dog will become habituated to it. Once this occurs, your dog will be less motivated to respond to your commands because he is used to the pain or unpleasantness of the aversive stimulus. At this point, you will have to escalate the force of your aversive stimulus, and this will increase wear and tear on your dog. To avoid this, apply the "proper" amount of force from the beginning (not too hard or too soft). The actual force needed will depend on the reason for the correction and on your dog's temperament. Get a professional trainer to show you the proper amount of force needed so that you do not over-correct your dog. If after an aversive correction your dog continues to misbehave or ignores a known command then your dog may not understand what is required of him, you are not applying the aversive technique properly (incorrect timing, inappropriate force), or your dog has already gotten habituated to it. Make sure you understand the reason for non conformance before proceeding with a fix.