When I was in undergraduate school, I had to take Personal and Community Health to gain my teacher's license. During that course, we had to pick a sport and write a term paper on some phase of it. Because I was such a movie buff, I chose boxing because there had been SO many movies in which boxing was featured, and I had seen many of them either at the movies or on TV.
May seem strange coming from the likes of a Broadway baby like me, but as I thought about the films (and read about them to do additional research, Manny Farber's excellent essay "Fight Films" was a major source of information), I gained a tremendous amount of respect for men who chose to earn their living doing this. It's not an easy life.
Anyway, I thought then and I still think now that the finest boxing movie ever made is THE HARDER THEY FALL, Bogart's last movie. I honestly like it better than ROCKY or RAGING BULL (neither of which had been made when I wrote that term paper). It contains the fewest cliches, tells a very interesting and involving number of stories about fascinating people, and contains some riveting performances from Bogart, Rod Steiger, Jan Sterling, and Mike Lane as the tragic boxer who's too naive to know what's happening to him. I also like THE SET-UP, a Tony Curtis programmer THE SQUARE JUNGLE, and CHAMPION (Kirk Douglas' first Oscar nominated performance).