pit bulls are one of the smartest (reasoning, not ability to learn tricks) most loyal, and dependable breeds out there. I've had several (some pure bred some mixes). I've also had many other types of dogs (hunting dogs, hounds, house dogs, guard dogs) well over 50 not counting puppys. so I've had alot of opertunity to compare.
the only real problem with them (other than bad publicity & moron owners) is they are the ultimate over-acheiver.
if you teach them to be a part of your family, raise them in the house with the kids, ect. they will be the most loyal family pet and protector of your children and family you've ever seen.
you can teach them to do stupid things, like bite a rope and swing from it until you tell them to stop. and they will hold until you tell them to stop or they pass out, they don't know quit.
but if you are a stupid, insecure, want to be toughguy(if you only had the guts). and you buy the bad bellybutton dog to prove something about yourself, chain it in the yard and abuse it to show off to your freinds just how tough and sycho-crazy you & your dog. that dog will over-achieve and be the most unpredictable and dangerouse dog you've ever seen.
but it doesn't just happen, you really have to work to make a pit freak out like that. put him on a chain, random beattings, or if the owner has a stability problem they will pick up on that too (most dogs take on their owners personality after a couple years.
there are dozens of breeds that are much more unstable, the difference is that the are mostly small and you don't go to the hospital when they freak out.
of all the dogs I've owned and been exposed to, poodles are by far the most unstable dogs out there.
some dogs are naturaly mean (as in more than 50% are unstable) but pits aren't one of them