Nonpareil Jack Dempsey was a total gentleman by all accounts I've seen. Charlie Mitchell also comes across really well.
Marciano broke the jaw of a guy that worked for him, dined with mob men, travelled the country with a suitcase full of **** and dildos partying while his wife sat at home. That being said, he always spoke of other fighters well, even ones he didn't like, and helped pay Ezzard Charles' medical bills. Patterson on the other hand was a gentle guy, once stopping mid fight to pick up his opponents' fallen mouthpiece, some even wondered if he was really cut out for boxing.
Maxie Rosenbloom apparently didn't like hurting people and was a bit of a womanizer, Henry Armstrong was a notorious womanizer, Ali was a real gentleman never putting himself above ordinary people, Emile Griffith was pleasant unless you called him gay which made him pretty angry, the only bad thing I've heard about Ray Mancini is when he threatened Quentin Tarrentino for turning him down for a film role. I think it's fair to say that most boxers aren't tough guys who puff their chests up, some, like Hearns and Hagler, are stand offish, some, like Duran, have a mean streak, but most I've met or know about are nice people.
That's probably because Joe seemed unsure of himself around cameras and in public, that oppressive management contract played a big role. He always seems awkward and even unintelligent, but away from the eyes of the white press he was a charming womanizer with a drug habit that got worse and worse after his retirement.