I don't know much about American Bulldogs, but I do know a lot about American Mastiffs. One of 'em is by my feet right now!
If you travel a lot (and have to leave the dog all alone for extended hours at a time) or are looking for a jogging companion for long trips, then an AM won't be a good fit for your lifestyle. But if you have the space in your yard/ home, aren't the kind of person to go on all-day hikes, and your weekday doesn't force you to leave your dog alone for 7+ hours a day... then I couldn't imagine a better dog than an AM.
They're super-sized (males routinely grow in excess of 225 lbs), super-smart, super-loyal, and super-healthy (12+ years lifespan is not atypical). Mine was completely housebroken at 10-weeks, never ruined any furniture or shoes with his teething, and doesn't have an aggressive bone in his body. I couldn't be happier with the breed -- or how helpful & accountable the AM breeders are.
If you have any specific AM questions, please let me know. Good luck!