It is impossible to know, really. There are too many variables - conditioning, natural ability, attitude and experience, among others.
It's a bit like arguing who the best athlete was in history at a particular sport. It's fun to argue about it (I do sometimes) but in reality it is pointless.
At any given time, the best gongfu practitioner might be better than the best Brazilian fighter. At another time the situation might be reversed.
I know I wouldn't want to take on a person who was good at either style.