Of retired boxers, either Saldivar or YCIII, whichever you rate the higher. If Uysk surpasses them, same 2, just whichever you rank the lower.
I think Jackie Fields is the most underrated WW in history, where I rank him #10 all time. He amassed an extremely deep win resume whilst only ever losing 3 fights there. 2 of those were to YCIII, who also beat Ceferino Garcia, Joe Glick and Jack Thompson. After losing his WW title the 5ft 5ins YCIII, already a tank at WW, moved up. Never much more than a LMW, he beat a fading Mickey Walker, the brilliant and much bigger Billy Conn, KO'd the excellent and also much bigger Gus Lesnevich before beating my #12 all time MW Fred Apostoli. Conn and Apostoli beat him in rematches, but going 1-1 vs these much bigger ATGs (ok, borderline ATG in Apostoli's case) is an incredible p4p achievement. I honestly think the best argument that YCIII isn't the 5th greatest Southpaw of all time, is that he's the 4th, ahead of Saldivar, who I rank #3 all time at FW. That's how highly I rate YCIII's career.
I completely forgot about Nazarov shamefully. He was a brilliant fighter, a bit better imo than the likes of Loma, Golovkin and Tszyu. On par with Arbachakov and Usyk as the best and most skilled of the post-Soviet era maybe. A real pity about his eye injury and the shooting incident. Loma probably belongs in the discussion for filling out the top ten to be fair. Overrated heavily in the scheme of things but still a brilliant fighter.
I forgot about Borkhorsor too. A horrible, skilled tank of a human being even at bantam. He must have been monstrous at flyweight.
That's a fighter that rarely gets mentioned but deserves some appreciation. He was a damn good fighter and a monster.
I'd like to say Michael Nunn, but he wasn't at the top for long enough. He was a top MW for maybe 2 years and SMW for maybe 2 more. I'd say Camacho, he was in the mix for at least a decade plus