1 - Joe Louis
2 - Muhammad Ali
3 - Larry Holmes
4 - George Foreman
5 - Lennox Lewis
6 - Evander Holyfield (best cruiser of all time by far)
7 - Joe Frazier
8 - Rocky Marciano
9 - Jack Johnson
10 - Jack Dempsey
With all this said... And I know a lot about boxing history. Wins and losses do not tell you everything. I would rank all 10 of these fighters ahead of Mayweather in a P4P all time rankings. And Mayweather is probably ranked 6th in simply welterweights from 1980 - present.
Wish ppl knew more about it all. He's not even really undefeated, Jose Luis Castillo beat him. IDGAF if the judges gave it to FMjr. Doesn't matter on paper, he lost that fight.
And Mayweather is the biggest bore in the sport. It would be like going to a movie, having no rising actions, no climax, no conclusion....... then being told by critics that you enjoyed it.