Deof SRR, Ali said it himself, and that's one guy who's never unduely modest
A lot is said about Ali's principles, but don't forget that when SRR was fighting, the mob controlled boxing, and the only one's who made it had to join with them. This is somehing that SRR and LaMotta refused to do, and as such had to force their ways to the top, despite not getting the fights they should have. This is the main reason they fought each other so much, there was nobody else!!
Also SRR was a true gentleman in the ring. Always respectful to his opponent's even in defeat. I would also say that he had everything as a fighter. I always felt Ali wasn't too heavy a hitter, something he said himself in the run up to the Foreman fight, "I don't hit too hard, but I'll out box him". (or something similar )