I scrolled thru the previous responses, and I don't think I saw anyone post what I will.
My favorite (original) series moment was when in Ep. 4, the Emperor's Throne room, Vader is pushing Luke's buttons with "If you won't turn to the Dark Side, then perhaps, she (Leia) will." Luke snaps.
What I loved was Luke took the fight to Vader, and won. Luke, was filled with anger, on the offense; Vader, was totally on the defensive, and losing. Having the VHS copies, I never noticed until DVD's widescreen was after Luke took Vader's hand off, Vader was holding his remaining arm up in a plea for mercy.
Of the newer series, it has to be the fight between Qui Gon/Obi Wan vs. Lord Maul. I was returning from a deployment in Saudi Arabia, and I had heard the new Star Wars was coming out with an epic fight scene, but I was pleasantly unprepared for the intensity of the two-on-one battle.