They are both bad, I will not say who I voted for, I will argue Vaders point for fun though.
He destroyed his
daughters home planet.
He chased down his daughter and sentenced her to death, would have killed her if his son didn't come in and save the day.
He was born to save the world but turned bad and severely weakened his wife before giving birth, pretty much killing her.
He cut off his
sons hand.
He killed
both of his masters. (Obi-Wan and The Emperor)
He killed his officers in his army if they made him mad.
He blew up a planet because he could. (badarse)
He tried to blow up another planet but his plan was foiled by his son.
Reminder: This is his son he is fighting, he is holding him off with 1 hand... His son is very clever though so he is tricked a few times here
http://www.youtube.com/watch?v=0iQwIJO16ms