"Assuming badder is even a word"!!! HAHAHAHA! For the record, it's "worse."
And I wouldn't really say "better darklord" either. It just doesn't fit. LMAO.
Anyways, I think Sauron is the worse one, but Voldemort is the wiser. =)
Sauron is really evil. He has them nasty nazguls. And the eye is REALLY scary. LOL. That's why I think he's the worse dark lord. But I wouldn't really call him smart since his only purpose is to get the ring back. Obviously the good characters learned that, and their only purpose is to destroy the one ring. It's just TOO easy to defeat him.
As for Voldemort he may not be the worse, but he's smart. He works sneakilly and secretly. He's not an obvious. And his purpose is not clear either. Does he want to take over the world? Kill Dumbledore, Potter, and all who's against him? Blah, blah... You know what I mean...