I think my limit is big dogs. The largest breed in the world gets up to 230lb/104kg. That's big, but I'm bigger. They also have some some weaknesses that other animals can't really exploit, but a human can. Just have to make sure you don't let them get on top of you and focus on their eyes, nose, and groin.
I probably don't win every time, but anything bigger than that is going to beat me 100% of the time.