By far the most common collar is the extraordinary bell for dog collar that fastens with a plastic clip or a buckle. These collars are the most convenient to slip on and off and are handy because they can hold your dog's identification, rabies, and license tags. Even though this type of collar retains its size, the collar can become a hazard. Dogs playing roughly and in a mouthy manner can get their mouth caught in the collar of another dog, causing panic in one or both dogs. As they struggle to get loose, the collar can tighten and dogs have suffocated as a result of this type of play. Dogs who are the object of this type of rough play should wear break-away collars, similar to the break-away collars in cats, at least during play and unsupervised times. Some owners opt to avoid collars or any gear at all unless they are taking their dog on a walk. Although this in an option, I prefer to have visible identification on my dog at all times and a collar with its tags is the most convenient way to do this.
So there you have it, an overview of a variety of common collars and harnesses. None is perfect. They are all just tools. But some are more likely to cause problems in your pet or may just provide a less than ideal match for your needs. In case you're wondering which I prefer—ideally my dog can walk on leash with the flat collar he wears regularly. But for those dogs that tend to pull and need more work, I tend to recommend a front-attaching harness or a head collar of some sort.