Duran had by far "better" footwork. And Duran was more skilled... not even close. Ali simply had flashier footwork.
It's hard to compare because Ali and Duran used foot work for different reasons , Duran should be compared to fighters like Frazier or Tyson . Ali should be compared to Robinson or Leonard...... Each style used foot work for different purposes . The former used foot work to get in close, cut the ring off usually had great body attacks and fought aggressively, the latter used foot work usually to keep the fight at long range usually behind a jab, setting up combinations, and counters.