Cuevas by KO. He was murder at his peak. Lopez is one of my favorites of the 90's, but the pick is Pipino here.
I'm gonna disagree with you and base it on which version of Lopez it is. The one who savagly took apart Campas stops Cuevas. JL threw beautiful combos in that fight and Cuevas would be there to be hit with them. Granted, Campas was NO Cuevas, but still, Pipino had no defense. Cuevas would definitely knock out the Lopez that lost to Page though.
I like Cuevas to possibly end ANY version of Lopez' life. You talk about versions of Lopez, well in his prime...Cuevas ate punches for a living and smiled them off. In a slugfest, without premise of defense, there is nary a welterweight who'd have ever beaten Pipino.
I admit I'm no expert on Cuevas' career, but I just don't see the opposition he walked through to suggest that he survives like that against anyone who can hit like Lopez, or who boasted his chin. I agree with X, I see the absolute best version of Lopez beating Cuevas. Any other version loses, and probably in violent fashion. But I'll favor him at his best (in which those moments were rare) in this one.