Roberto Duran vs. Tony Ayala at 154. Fight almost happened before Tony went away. I think Duran would have been motivated and would have won in the later rounds.He was a better defensive fighter. Duran did not get hit cleanly very often.Great head movement.
I think Tony Ayala would be very competitive over about the first 6 rounds, since he was a real pressure fighter who's hands were perpetually throwing punches. After that though I think Duran would take control and begin dominating on the inside in route to an 11th round stoppage.
In the 1980s KO magazine (or one of its sister publications) did a piece on this fantasy could-have-been/should-have-been match up. They had Duran stopping him in about 9 and I'd go the same way.