You know, while the old movies make the new ones look rather bad, the new ones make the old movies lightsaber battles look kind of boring...
Anyway, I still think that Obi-Wan and Qui-Gon versus Darth Maul is still the best lightsaber duel. It's the one redeeming quality to the Phantom Menace. I did really like the fight between Obi-Wan and Anakin, though. I think Maul's general look is what edges it out for me.
Some of the other fights in Revenge of the Sith, though...gah. I was expecting so much more of the fight between Palpatine and Mace, Kit, and the other two Jedi but it just came up short. The same with Grievous. I didn't mind Palpatine laying waste to four Jedi, but Palpatine flipping around just doesn't look right; I wanted the battle drawn out more, the opportunity to see the rather confident Jedi suddenly go "Oh...my...lord. We're screwed," and turn to desperation as Palpatine successfully fended off and started killing four Jedi. Similarly, Obi-Wan took out the vaunted Jedi killer Grievous far too easily - maybe I was a bit overly-expectant, though, thanks to the Clone Wars cartoons.
In either case, yeah. The Maul fight scene tops them all while Obi-Wan and Anakin comes in close.