To me it is tied between Vader and Luke in Empire Strikes Back and Return of the Jedi, though ive always thought the empire duel the best, i still Love it in ROTJ when Luke just goes nuts on Vader.

Luke gets owned in Empire Strikes Back, and when they duel at the start in Jedi Luke and Vader are equalls, but because Vader is an old man and mostly machine Luke Bests him.

If it had been Luke Versus a Non cybernetic Vader the results would have probably been far different.

The Luke in the original trilogy could never best any of the old jedi from the fallen order during the old republic, But the Superhuman Luke from the EU who can seemingly cleave a stardestroyer in half with his lightsaber could take even prequel Anakin.