Gotta go with Starkiller. He witnessed his own father being murdered in front of him by Vader, was raised to be the perfect assassin and murdered some of the most skilled Jedi in the galaxy. He also was betrayed by Vader TWICE and absolutely demolished him in the Death Star, then Vader tries to clone Starkiller because of how powerful he was, hell he even stopped a star destroyer. Then the clone version of him beat down Vader as well. Not to mention starkiller's outfits, that sith armour you get looks badass.