There are guys who have reputations as not being overly violent.
I mean, Joe Ligambi or John DiFronzo probably aren't malicious guys at all.

The nice guys probably don't get in much trouble, so we never hear about them. So it's hard to name a guy who was really a good guy. From reading books about the mafia i'd say maybe Sonny Black. He supposedly had his wife call up Pistone and tell him he wasn't mad, and then he went and got killed. Thats a lot nicer than I would have been.