Frazier kicked Ali's ass twice. He just happened to win only one of them (he beat Ali to a pulp, and then his one good eye sealed shut and he fought blind for the last 3 or 4 rounds). Frazier was a damn warrior.
I thought somebody might bring this clip up. It is absolutely hilarious. Louis was 37 when he fought Marciano, who was only 27 at the time.
I just absolutely love that scene, and the movie as a whole so I couldn't let it slide by without posting it, even if it was the obvious choice.
I absolutely love boxing and can talk about these things for hours on end and never get tired of it but it really is just a toss up between a handful of guys. For each one you can find a staunch group who will argue their point of view to the death. You'll never convince an Ali guy anyone was better, same with a Marciano fan. From what I've read, I think it's not out of the realm of possibility to suggest that Jack Johnson was the greatest of all time.