I've always like Buster Keaton a lot more than Charlie Chaplin. Chaplin would get sappy at times, while Keaton just went for the jokes, and his physical comedy is top-notch. In the modern era there is Jackie Chan, who comes close to Buster's stunt level. These are some of Keaton's better stunts, with explanations as to how they were done.
Above is a video with clips of both Charlie Chaplin and Buster Keaton boxing. The differences in their approach to the humor of the situation is obvious. Chaplin is a trickster, frequently outsmarting his opponent whereas Keaton is a complete stumblebum.
I've never been a big Chaplin fan, thinking many of his jokes are too cute for their own good. I much prefer Keaton's physical humor -- his getting tangled up in the ropes trying to enter the ring is good example of his work.
