If you're going to make Sauron at the time of LotR fight Darth Vader then of course Vader is going to win. That's like making a full-strength Sauron fight Vader after Luke had removed his helmet. If the two fought at the height of their power, then Sauron would win.

Anyway, they were both just minions of a more powerful and evil master, so clearly Paris Hilton.