Darth Maul saberstaff action in Ep. 1 was probably the best choreographed, and Obi-Wan vs. Anakin in Ep. 3 had the best action, but my personal favourite was Yoda vs Dooku at the end of Ep. 2. Seeing that for the first time just made the whole movie right there, with his "Super-Grover" battlecry and his hopping around and bouncing off the walls. No other lightsaber fight really had the same OMFG impact as seeing that for the first time, because even though you know Yoda's a Jedi Master and everything, it's the first time you've ever seen him really move and fight like a Jedi Master. Great stuff.
Be considerate to others or I will bite your torso and give you a disease!