Darth Vader FTW.
Why I think so:
Vader is a master of the Dark Side of the Force, and a Sith Lord. Sith Lords don't simply rely on raw force power. They use cunning, guile & deception as well.
Didn't anyone watch "The Empire Strikes Back"? Didn't you see how much effort and preparation Vader put in into luring Luke Skywalker out from Dagobah all the way to Bespin?
Don't you think he'll put in even more effort to ensure he has the upper hand against such a formidable foe? He may not be able to harm Superman directly, but he can threaten to harm everyone else around him. And Superman would eventually have to submit. Aside from kryptonite, compassion is another of Superman's weaknesses. Unless he drinks Johnny Walker Red Label like in (the original) Superman 2. That stuff will turn anyone bad......
Of course, one may argue that Lex Luthor & other have exploited that weakness before, but then they all had bumbling idiot sidekicks & underlings. Vader's men are creme-de-la-creme Imperial Stormtroopers.
Gawd, I need to get a life......