It was a composite. Although TB would disgree, I think Vito was primarily based on Joe Bonanno.
I saw a program on OC that said Joe Bonanno would meet with people every Tues and Thurs. and listen to their personal non-mob related problems and do favors. The description was exactly as depicted in the opening scene of the movie. I don't know if any of the other major bosses regularly did this though. Of course the similarities would end with Vito's ban on drugs.
