Even within specific pure breeds each dog has its own personality on top of whatever general traits the breed has so it's a bit of a lottery really. Pit bulls have a 'reputation' and I have to say I wouldn't trust one even if it's "the sweetest dog in the world". They were originally bred to fight and I believe there is still a latent attack instinct buried deep in the genes. It may not always show itself and some pit bulls are absolutely great pets but whenever you hear of a kiddie's face being chewed off by a dog it's almost always a pit bull, a rottweiler or a mutt with those genes. It's not a coincidence.
I know this point of view isn't popular with pit bull owners who will leap to the defence of these dogs but when there are so many alternative breeds I don't understand why people choose them to be honest. Apart from the shaved and tattoo'd morons who like to strut around with a pit bull on a chain to prove how 'hard' they are.