American Staffordshire(AKC register) Terriers are the same as an American Pitbull Terrier(UKC register), granted a "TRUE" Staffordshire is much smaller that what we know as American Pitbulls. Staffys run 30 to 40 pounds while the other 2 (1) can range from 50 to 90 pounds.
Now an "American Bully" is a whole different mix................Short, low and wide. Kind of like the low-riders of the bully breeds. I think they are now a legit breed of their own. Originally the ""game"APBT crossed with an English Bulldog, they are cool to look at but not too much for endurance.
Now they are also doing tri-colors like a rottie.