He was champ in perhaps the worst Heavyweight Era of all time (early 1980's) someone like Lennox Lewis would smash him.
I rank him number 6, barely behind Lewis but they switch spots often. His longevity alone is amazing and combined with some good performances against some very good fighters such as Shavers, Cooney, Norton, Mercer puts him easily in the top 8 in my opinion. Head to Head he gives a severe problem to every great that ever lived. He had the best jab of all time, was a warrior in there and his recuperative abilities are second to none. Apart from his jab he didn't have a lot of great weapons although his right uppercut that he took out Weaver with is very dangerous, and his right hand wasn't bad. I do hold against him though that he didn't fight many of the top fighters of the era such as Thomas, Page, Coatzee, Dokes. He had too many easy defenses and that drops him a spot or two, although like I said he deserves to be top 8 on any list. He also failed to give rematches to his toughest challengers.