Visually appealing for sure Josh, I voted ROTS Obi-Wan and Anakin based on this:
Total Screen Time
Emotional Stakes
Dueling Moves
Now as far as moves, I'd go hands down with my boy Maul as the most amazing stuff, but looking at the duels together, I notice one thing about the TPM duel, it's probably the only Jedi on Jedi/Sith duel that doesn't have an emotional stake to it really, they were helping the Queen and as Jedi, taking on Maul was more a responsibility, they didn't know him, there was no past between them, but all the OT duels had emotions running in the characters involved, there was some emotion in Obi-Wan and Anakin with regards to Dooku in AOTC, and there was a past there, and certainly ROTS's duels were filled, even the Mace duel, there were high emotions there.