Ok, lets put these things in perspective. Sephiroth wants to be the most powerful being in the universe. He goes around and tries to act hard. He doesn't kill many people with his hands or his sword. The you have Darth Vader, who kills for pleasure, who slays the entire Jedi Council, who kills the entire kid jedi school people. Hahaha, he slays the innocent children, if this is a contest of who is more evil, Darth Vader wins my vote.