They didn't fight at CW though. I mean, I can't count LHW who would have fought a SMW if they had a shot at it.
The orginal question I find hard to understand. Im basing my awnser on who's the best "pound for pound" fighter for each weight class in boxing history against other opponents in their division. I'd also say Ali at heavyweight.
Leonard never fought at LW. To answer your question: TWO answers and both in the same division. Roy Jones was the best SMW ever. Miles ahead of second best Joe Calzaghe. And Joe Calzaghe is/was miles ahead of any other SMW As CHJ points out, it is IMPOSSIBLE to overrate JC.
No, not miles ahead. H2H against a vast variety of opponents that would either be at 168 or moving up to 168, they're dead even because I'd pick none of them over either of them, with Jones beating Joe and why I rank him over Joe. Roy can move up to 175 and beat guys that Joe would not however, likewise to CW. KG mentioned that he'd pick Nunn over Jones at 168, I'd pick Nunn to get utterly mauled against JC at 168, mostly due to styles.
Holy CW Lopez 105 2-Sharp 112 RJJ 168 If BYRD would fight @Cruiser I think he can be close to Evander
Jones at SMW and Holyfield at CW are obvious picks (lol, I think like 20 people already said it) but they are flawed picks. The truth is, while they were clearly by far the most dominant ever in those weight classes, those are also two relatively new weight classes. At SMW and CW there isn't the same history as a lot of the other weight classes. It seems very likely that the best choices for this question will be in the "jr" weight classes. By that I mean, any of the newer weight classes really. Jones Jr and Holyfield seem to obviously be the right answers now, but I mean, with weight classes less than 20 years old, it seems too easy.