There are LOTS of different harnesses out there. It all depends on what you want the harness for!
A regular harness — that distributes the pulling force across the chest and shoulders — can actually help your dog pull harder. In my situation, I’m just looking for something that Moose can’t wriggle out of. So if a harness fits snugly and prevents him from breaking free, I’m happy. Small dogs can’t pull against a harness very well — they are too low to the ground — but medium and large sized dogs can use the harness to tow some pretty big loads. We’re talking person-sized and beyond.
Regular harnesses are great for dogs that have had neck injuries or who are prone to breathing problems — where a collar can put pressure on the throat, a harness puts the pressure on the chest and shoulders.
There are “no-pull” harnesses available. These can put pressure on different areas of the chest and armpits when the dog pulls. You do need to be careful if this is the type of harness you choose — a no-pull harness can cause abrasion in the armpits (between the dog’s front legs). There are lots of other options for teaching your dog to stop pulling; a harness may not be the best or easiest way to do it.
The leash can attach to different places. I’ve seen harnesses with the ring in the front, so that collar and harness can both be clipped onto the leash. Other harnesses have the ring in the back, usually between the shoulder blades. If your dog always walks to one side of you, a front ring may not be a problem. However, if your dog tends to wander, a back ring may be easier to keep untangled.
The most important thing is the fit. You don’t want a harness that will chafe the dog — whether under the legs, on the chest, on the shoulders, or across the back. If a harness is too tight or too loose, it can rub the dog painfully. Some harnesses are padded in a variety of materials, like fleece, foam, and sheepskin. But if you get a harness that fits correctly, you won’t need the padding.