I'm going with Bane in sabers and all out, though barely, and Kun in Force, though barely.These two mastered their respective saber styles to a level not seen before. Both had unique weapons, and both used esoteric force powers.
Darth Bane (as of DoE) has a very good chance of winning. I've grown more respect for Bane recently, and therefore I shall make a case for him. darth bane has the clear physical advantage, being stronger and faster, though the latter may be only barely. In terms of lightsaber ability, i'd say they're about equal. Now, in terms of force ability, Bane has lightning and Kun has amulet blasts. I'm not sure who to give the edge here, but exar did have complete mastery over his amulet blasts (I believe at one point he uses a blast from his eyes, like superman), while Bane's lightning is also extremely powerful. I give Bane the advantage here, though very slightly, because his lightning is more practical.
__________________ ”You presume limits to my power. There are none.”