#1 Ezzard Charles #2a Moore and 2b Spinks are close #4 Foster Jones , Beterbiev and Moorer aren't in the same rank with those 4 at light heavy
If Charles is deliberately not an option, then I'd be forced to choose Spinks. He's tall but can infight, he's a master boxer who can you knock anyone out, he's a defensive master with a very good chin and despite the impressions you might get from the Tyson fight - Spinks was a giant mentally. The Qawi fight is among the most impressive showings of mental toughness I've ever seen - and if he can beat Qawi like that, who can't he beat?
I honestly think that Charles has to be the #1. He went 3-0 against the man who might just have the second best case for that accolade. He is the only man who spent a lot of his career at 175, who still has a credible case for being a top 20 all time heavyweight. What an incredible fighter. If you are not prepared to consider Charles, then Moore and Spinks are the two names that you should be looking at. Incredibly Harry Greb probably belongs in the argument.
Gun to my head, i would choose Ezzard Charles. That being said, Bob Foster is a hard hard man to beat. 6'3 with a razor jab, strong right, quick hands and a pulverizing left hook. Hard to beat. His opposition wasn't the best but he was a glorious fighter. Spinks is probably the most well rounded and has the best combination of height, power and skills.