For longer reigns, Wilder is going to be up there. Martin and Stiverne were poor. Poor era breeds poor champions shocker, I guess.
Martin, Stiverne, Braddock and Seldon are good shouts. Marvin Hart. Leon Spinks. A few of the mid-80s crew. Shannon Briggs. Trevor Bryan. Probably a dozen total who fare atrociously h2h if you had them run a gauntlet against contenders from other eras.
Usyk . Do not remember any other belt holder with a overall legacy of only a total of 5 hw fights against only 4 opponents where only one of them was at the time of fight a top 10 at all ! Was there ever somebody else a world champion with such a pathetic record ?
So 40% of his fights were against a top 10 fighter.....probably a top 5 fighter. Fairly decent imo....have another try
Charles Martin is the clear number 1. Only ‘won’ the belt in the first place because of the eliminator he fought prior. And even then he only won that because Glaskov (or what ever he was called) blew out his knee early in the fight and had to retire from the sport, A truly awful champ.
Valuev was by far the worst boxer who ever hold world title, P4P. However, his size and (always) favourable judging might have allowed him to win against some of the weakest belt holders. Guys like Martin, Stiverne, Seldon definitely deserve to be mentioned here as well.
If I ponder the question like this: which heavyweight champion would, at his best, beat the fewest of all the other HW champs throughout history at their best... then I can't help but think of Marvin Hart!