I like this question, jreuter. Good move, by the way, in trying to pre-empt sarcastic responses.
Let me say that for prizefighters. Ali was probably "The Greatest." I don't have any problem with that. If the contest were a straight, Queens-de-Marquis (is that how it's spelled?) boxing match, then the edge would have to go to Ali, for his much greater height, weight, physical strength, and reach.
If the contest were a no-holds barred contest, in which one is allowed to use other parts of the body as weapons, then the edge would have to go to the great martial arts master, Bruce Lee, obviously. As far as I know, Ali had no experience in that form of fighting.