Here I was going to say: Peter Mandelson!!
Anyway, out of your choices:
Darth Vader - no, because he was repentant at the end, and Darth Sidious was the real big bad, even if many don't accept it.
Lord Voldemort - no, because he was a spoiled brat as a kid who never emotionally matured, slap him a couple times and he's fine... after a fashion.
Dracula - all he's after is a stonking great orgy.
So, I'ma go Sauron (though he's got his backstory... as mentioned).