Harry Wills has a deeper win resume than Jack Dempsey, but is rarely ranked ahead of him, so he's my answer.
I think most people on this forum credit him, but outside of the more learned corners of the internet I’d think few appreciate Archie Moores’ credentials at heavyweight.
Ezzard Charles, forever in the shadow of Joe Louis. Elmer Ray split with both Charles and Walcott Larry Gaines beat Schmeling, Carnera, and Godfrey. Very good career.
Leotis Martin is underrated, for me. He was forced to retire after the biggest win of his career against Sonny Liston in Las Vegas in 1969 (suffering a detached retina). They say Martin's 10-rounder with Thad Spencer at the Albert Hall in 1968 is one of the best heavyweight fights ever seen in the UK. Sadly, it wasn't televised. Nino Valdes is also underrated.
I agree. Leotis was a big puncher considering how small he was. He was lined up to fight Frazier in an all Philly battle but had to retire because of the eye injury sustained against Liston. I think Joe would have beaten him but Leotis was tough as nails and would have pushed Frazier hard had they fought.
Sultan Ibragimov is my choice. That guy would have been hell had he fought in an earlier era. He didn't do well against Klitschko but I was always impressed with his skillset and boxing IQ. The size of Klitschko was an issue for him as he really was a cruiserweight.