Leonard beat the other 3 kings of his era, Hearns, Duran, and Hagler. Mayweathers resume doesn't come close to that.
Depends on your preference. There was another good thread about this and my ultimate conclusion was that Leonard had the higher highs but FMJ did a lot more. Pretty Boy Floyd had more title fights before switching to Money than SRL had his whole career--13 for Leonard and 16 for FMJ pre-DLH. Floyd's record has a lot of great wins and lacks some of the controversy and later humiliation that SRL put himself through. SRL fought better fighters closer to their peak though and has a much higher tier of competition and wins. SRL vs. Hearns I, Duran 2, Benitez and Hagler are a cut above Floyd's best work.
There is no preference Leonard beat legends and not only that they were undefeated prior to meeting Leonard.
Fair, balanced post. I voted SRL, but a sensible argument can be made for Mayweather. It depends whether you prefer quantity (Mayweather) or quality (SRL) of best wins.
Leonard's top 4 wins over Duran, Hearns, Hagler, Benitez, surprass any of Mayweather's best wins by quite some distance. But Mayweather has much more longevity and a considerably more quality wins overall. As @Greg Price99 said its whether you prefer quantity or quality but its not like Mayweather is short of quality though either TBH but I think he lacks wins over ATGs in their prime compared to Leonard.
Leonard's list read like a "who is who" of 80s ATGs. Furthermore, Leonard took fights where he didn't have the upper hand or he was even the underdog. Fairweather has nothing like that in his resume. He had many good fights, but he always tried to get every possible advantage, up to the point of voiding some fights of any substance. Such was the case with the fight with Pacroid. By the time the fight happened it didn't make much sense. Not that Leonard didn't try to get things his way. Every fighter tries it. But Fairweather went over the line.
I voted for SRL . Hagler,Hearns,Duran and Benetiz had a combined record of 204-3-3 when SRL beat them. Hearns and Benetiz had never lost and Hagler and Duran hadn't lost in 10 years