I think, by default, Ali. If he had not self destructed, Mike Tyson had the potential to be the best fighter by far, he was simply devastating in his prime.
My father and I never agreed about Ali with me. He felt Ali was a draft dodger and that made up his mind for him. He also never understood how I, as a Marine, could feel differently. I didn't agree with Ali, but felt that he was sincere in his beliefs, so I admired him for it. He could have gone in the Army and he would never have seen battle. They would have made a poster boy out of him like they did with Joe Louis. So, I feel he gave it all up based on principle.