My money is on the Pit Bull:
I work in a town where a lot of the young "people" (being nice), have Pit Bulls. It's kind of a status symbol, if you know what I mean. Well anyway, I've been attacked by a few of them, and over the years our department has shot about 10 of them when they were attacking officers. (actually some were ordered by the owners to attack) Several of them have survived being shot more than once at close range.
Pit Bulls are fast as lightning, bite hard and don't let go, and go for the throat. They also have large, very hard heads and deep jaws. When one goes bad, they are a very "bad" dog to deal with!!
(I should point out that they are bred by the owners this way. They can be the nicest dogs in the world, but not the ones we deal with)
I love dogs, and it breaks my heart to see how some of these dogs are raised.
Wolves are pack animals, and rely on numbers.
Don't know if you wanted a serious answer, but there's my $.02
Joe