Leonard. Duran certainly wasn't powerless at the weight. In fact he was still heavy handed and had that great timing. But on the whole I think Leonard had the edge in terms of speed and ability to one shot a guy at this particular weight class. When Duran knocked guys out at welter, it was through accumulation rather than one or two clean shots.
Duran slightly. He was able to hurt the iron chinned Ray Leonard and even put Palomino down at that weight. I don't recall Leonard really hurting Duran in their fights at Welter.
Sugar Ray Leonard by far. Leonard decked and stopped champs like Benitez and Hearns, wiped out top contenders like Dave "Boy" Green, Andy "Hawk" Price, and Pete Ranzany. Who did Duran stop at the weight? Wellington Wheatley? Please.
And they were usually guys you never heard of before or ever again. How many Wellington Wheatley or Joseph Nsubuga fights did you see before or after that? Those are the guys he stopped at welter.
Duran more likely to knock you out after a sustained heavy beating, Leonard more likely to hurt you with that one punch and follow it up with combinations to end it.
And yet, Duran hurt the iron chinned SRL with a punch he didn't set his feet on or pivot or really anything one does to generate the most power. Yet Hearns and many other fighters never hurt SRL like that before or after. How does that fit into your little formula?
Duran landed one punch in like 35 rounds that wobbled Leonard for a split second ... in what was probably the greatest performance of Duran's career ... and that's YOUR little formula? Hearns dropped Leonard twice in their fights. And Hearns was dominating Leonard through much of their first fight and closed his eye. Duran never gave Leonard the trouble Hearns did. And Duran never knocked out anyone at welterweight worth a damn. Leonard did ... in Hearns, Benitez, Green, Price and Ranzany. THAT's the formula. Leonard hit harder at the weight.