not best...I don't want to get into what's better than what. You can list your Favs, underrated gems, forgotten flicks..etc.
If doesn't necessarily have to be boxing intensive with a lot of fight choreography...it could be about a boxer(i.e. The Hurricane)
The Champ(OG)
The Harder They Fall - Bogart tries to turn a giant untrained Argentine into a competitor
Requiem for a Heavyweight - Anthony Quinn plays an old boxer trying to adjust to life after fighting
The Great White Hope
The Great White Hype(I have to give this a fresh viewing tho)