Dog Training Collar

A dog training collar is most effective when it fits snuggly and high on the dog's neck just behind his ears. If it is too loose the collar will slip down the dog's neck and rest just in front of the shoulders where the dog is the strongest. Giving a check in this area is extremely ineffective.
This is why the choke collar is not the best choice for a dog training collar. They slip over the dogs' head, which means they have to be loose enough to fit over the ears, which usually makes the collar too big.
A Better Training Collar
Perhaps the best dog training collar choice is the snap collar with both a live ring and a dead ring component. This collar is the most versatile training collar.
Because it is a snap around collar you can fit it precisely to your dog's neck. It's possible to have it sit high on the dog's neck just behind the ear where it is most effective. You should allow one and a half or two finger spaces between the collar and your dog.
These snap collars usually come in braided nylon or leather. Since they are not adjustable, it is important to measure your dogs' neck precisely to achieve the correct fit. Some pet stores allow you to bring in your dog for even more precise fittings.
The beauty of these training collars is they have both a live ring and a dead ring. If you connect the leash to the live ring (the one that isn't floating) and the snap part of the collar is attached to the floating ring (or dead ring) then when you give a check on the leash the collar tightens on the dog's neck and causes an unpleasant experience. As soon as tension is released the collar returns to it's original shape.
Best of Both Worlds
When you aren't training you can clip the leash to the floating ring and have the collar snap attached to the live ring and now the collar has been transformed back into a basic dog collar.
Since this is a training collar, don't be tempted to attach identification tags. These will only get in the way and cause problems when your using the collar in training.
The Choke Collar
Another dog collar choice is the choke collar. The choke collar is usually made of metal ringlets strung together. There are varying sizes of ringlets ranging from small to large. The smaller the ringlets the smoother the action of the collar will be.
NOT designed to Choke
The collars are called "choke" collars because when you give a pull on the leash it tightens the collar around the dogs' neck giving him an unpleasant experience. If used correctly, the choke collar really shouldn't do any choking. If you have constant tension on the collar, then yes, it will choke your dog.
The collar however, is designed to tighten and then immediately loosen as soon as the tension is relieved. The smaller the chain ringlets the quicker and smoother the tension and release action will be.
Keep in mind that because of the potential for choking, never leave your dog unattended while he is wearing the choke collar. Also since the ringlets are designed to move through the "dead" ring, you shouldn't attach any kind of identification to the collar such as dog tags. The tags could hinder the tension action, rendering the collar useless.
The BIG Problem
The problem with the chain choke collar is that it must fit over your dogs' head and hang around his neck. Since a dog's head is usually wider than his neck it will not fit snugly and will tend to hang down around where the dogs' neck joins his shoulders. This area is one of the strongest parts of a dog. If you are trying to check his behavior when the collar is in this area you will likely have no effect on the dog.
What will likely happen is your dog will end up pulling you around wherever he wants to go causing you frustration. In your frustration you may give too strong a check and damage the dog's trachea or neck.
Another problem with these collars has to do with their alternate name, slip collars. They are designed to slip over a dogs' head to put them on, but this also means a dog can slip out of them quite easily. You could end up with your leash attached to the collar but your dog running around free; obviously not the intended result of the training collar.
Choke chain collars are some of the most widely used collars out there, but they have the most capacity to injure your dog and are not as effective as many other choices.