Qui-Gon and Obi-Wan VS Darth Maul is one of the few memorable parts to come out of the prequel trilogy, if not the only. I liked it back in 99 and like it today. Sometimes I'll go back and watch just those scenes.

Forget AOTC.

Obi-Wan VS Vader in ROTS was all flash with no substance. Only the enviroment itself is what kept my attention from wandering in '05, and today I never watch it all the way through.

Obi-Wan VS Vader in ANH is cool, albeit pretty sluggish in parts.

Luke VS Vader in ESB is spectacular all around. Vader really comes undone and lays down the law on Luke, who manages to hold his own for quite a while.

Luke VS Vader in ROTJ is one of the few watchable parts of the film, but I still prefer the ESB duel.