Luke vs. Darth in ESB.
For some reason, the three-way fight in TPM never cliqued with me. But the Luke vs. Vader fight had a dark rythm to it. It was as if Luke was fighting with the Devil himself. And Vader was in top form, regal and menacing, disappearing into the shadows or using the scenery as a weapon. Plus Vader's leap is like a vulture swooping down on his prey, unlike the Maul/Jinn/Kenobi Olympic Gymnastics flips.
Plus the Luke/Vader duel ends with one of the most memorable scenes of all time.
Had Lucas opted to let Maul live until Episode III, then have Anakin take down Maul in his rise as a Sith Lord, that might've rocked. But only with Vader in full masked panoply.