Based on resume the rule is- 1. Louis 2. Ali 3. Langford 4. Wills 5. The rest with Jack Sharkey at about 8.
Based on resume in what fashion? Record? Title Defenses? Those are easier to come up with definitive answers for. Once you start subjectively comparing quality of opponents, etc, it becomes trickier and is more subject to opinion. For example, based on resume, how do you rank the following three: Marciano, Louis, Holmes ?
Those three are pretty clear-cut to me: 1. Louis 2. Marciano 3. Holmes Louis faced an extraordinary amount of top ranked contenders, over 30. And he only lost twice, knocked 90% of the rest out and whenever there was any doubt as to who was the better man, he always gave rematches and always knocked his opponent out in it. Marciano is second because he was so dominant. He gave every deserving challenger a shot (his title reign: 5 times the #1 contender, once the #2 contender). Not only that but he knocked every single one of them out. No one in the 50 years before him or the 50 years after him has ever accomplished that. You can say that his opposition was not that good, but i think it was very good: Walcott, Charles and Moore were all extremely tricky fighters with 60+ fights under their belts. A guy like Holmes fought lesser opposition as a champion if you ask me but he wasn't half as dominant as Marciano was. Holmes is third because he left a lot of unanswered questions and frustrated fans during his reign. To rank higher than Louis or Marciano, he should've fought at least a few of the deserving challengers that he failed to meet (Page, Thomas, Coetzee, Dokes). He also avoided every rematch in close fights with Norton, Witherspoon and Williams, the last two could've gone either way and he should've given rematches if he was a true champion. That hurts his legacy. Outside of that he has a great resume though, and i do rank him very high (top5 usually) but the above shortcomings as champion disqualify him from the top4 for me.
I wanted to get a resume based on names more so than achievements/head to head. But it should be done in foresight as opposed to retrospect.