Thanks for the complement. I know I have too much time on my hands... Anyways, the most powerful was technically Anakin Skywalker, but he never reached his full potential. A better choice would be Lord Revan. He was a Jedi who almost single-handedly destroyed the Mandalorian Empire (and killed Mandalore in single combat, taking his helmet), until he turned into a Dark Jedi. He then proceeded to turn against the Republic and Jedi order, nearly destroying them until his mind was wiped. He then turned against the new Sith Empire he had helped create, killing several Sith Lords and destroying the Star Forge. What happens next depends on how you played the game Knights of the Old Republic and whatnot (I haven't), but he does even more. Also, he, like all Sith Lords of the past, was a masterful duelist, and would be completely able to beat any Jedi of the New Jedi Order in a duel (yes, even Luke).