Just in my experiences of dealing with them as they come to board:
The one constant is that they are *stubborn* little buggers when they want to be. It's almost impossible to get them away from something they really want, be it another dog, a leash or a toy. There is a pair that comes in that I absolutely hate. The female loves to chase other dogs and won't quit, even to the point of getting sick because she's running too much (the owner has overfed them to the point she looks like a basketball with legs anyway). The male has a fixtation on leashes or any hanging object (including my braid) and will not leave it alone, which means I have to tuck my hair into my shirt when I go into their room or he will grab it, he will grab and not release leashes and he is the messiest dog I've ever met. Simply incapable of keeping a clean room. Another "bad" one I've met was still a puppy and had a fixtation on a Vizsla puppy, so she loved to grab this poor dog by the side of it's neck and drag it around. Nothing short of confining her would induce her to quit.
The good ones I've dealt with are fairly cuddly and can be quite calm, lazy even. There is nothing "cooler" than a mellow bulldog.