Good Lord... I could buy this one either way but am going with Leonard. Let me think some more the reasons for this.
Ortiz was a great fighter but it's pretty tough to justify anyone beating Leonard at lightweight. He was probably the greatest fighter who'd ever lived up to the point he retired - and I include Gans, Langford and Grebb in that view.
Jesus. Probably Benny, you know? I could definitely see Carlos taking one in a likely series though, especially if they were facing each other more than once on the way up ala Leonard -Welsh. You couldn't beat Ortiz stylistically, that book was never written. You just had to be better than him - incredibly frigging difficult - or catch him on an off-night. Benny was one of the tiny few who was probably a slim shade better, best for best. And one of the even tinier few who has an argument for being more dominant against similar/slightly better opposition. Ortiz would've been his greatest opponent at the weight though and I'd imagine any fight between them to be close with Leonard probably playing matador rather than trying to drive Ortiz onto the back foot. I love Carlos, but best for best I'd probably take Leonard on points by a couple of rounds with most rounds being closely contested and Leonard's reflexes making the slight difference.