Hmm Darth Traya is a master in manipulation, not to mention very strong in the force and capable of using three lightsabers at the same time. But Darth Sion is fierce warrior, great swordsman and pretty much immortal. If it's a duel I would vote for Darth Sion, he would charge towards her no matter what, and he will keep standing until he kills her.
"Evil is a word used by the ignorant and the weak. The dark side is about survival. It's about unleashing your inner power. It glorifies the strength of the individual."