that's a bit tough to answer because I don't really count on-off type deals as having really trained someone (ie roach with hopkins and Oscar). I think being with a fighter through at least 3 fights should be part of the criteria
Steward, he can turn a decent heavywieght into a good Heavywieght. He also has one of the best win records in Heavywieght title fights, I believe its like something like 15-2. He has trained Holyfield,Moorer,Mccall,Wlad and Vitali Klit to championships.