Well, I can say managing a daycare that (gladly) accepts bully breeds, I have had the "daycare just isn't the best place your dog" talk with a disproportionate amount of owners of pit bull type dogs. We have NEVER had a human aggressive or sketchy pit bull type, but we have had several pits who presented with some type of dog aggression that made daycare not an option. This does not surprise me; I'm a great fan of the breed/type and well aware of their tendencies. We still give the breed/type a fair shake at work, though.
Very often, unfortunately, the dogs appear to be totally dog friendly to their owners, because their owners only see them play with 1 or 2 dogs. And with 1-2 dogs, they're fine. But the thing about bully breeds, IME, is that their arousal threshold is low, and they go from playing to fighting quickly. For many of them, daycare was just way too stimulating, and they went from "let's play" to "let's brawl!" far too easily. And then it can be really to hard to get them to come down from "let's brawl!" For these types of dogs, half the time, fighting IS good times, so it's definitely shades of gray vs. black and white. Which, again, can make them difficult in a daycare setting.
That said, most of these dogs are not leash reactive and probably very capable of playing with a few dog friends (supervised). Just not good for daycare, which is a very specific environment.
We've never had one that was human aggressive, however. Most are absolute joys when it comes to body handling, etc, and you can get them out of a scrap quickly knowing they won't bite you. Even the pet bull, street bred types have been pretty dependable with people IME.
ETA: We did have one dog that I sent home permanently because I suspected he was about to get very serious with other dogs. He was a petite (35 lbs) solid black little dog who looked very much like a classic APBT that had come up here from "a shelter down south". Gorgeous dog and in absolutely amazing physical condition... and totally ready to rumble with the other dogs in that unique APBT way where you never doubt they're having fun, LOL. Too bad, he was a gem with people and sooo cute.