I think Walcott edges him (post WW2). Joe was too shifty and tricky, and also too dangerous a puncher. He had a tricky, again...shifty is the word...rhythm...and was less predictable than Louis, for example. Prior to the war, maybe it would have been in Billy's favor.
I saw an absolute prime Joe Walcott ko a young sensational ko artist Tommy Gomez in 1946, and I think that JJW a true heavyweight, should be a favorite over any lightheavyweight in modern times. The rule still applies, that "a great big man beats a great smaller division fighter". So Walcott at his best beats any 175 pounder IMO...
same, louis was at a style disadvantage v conn, walcott is the opposite, probably more advantaged than louis was disadvantaged tbh.