Vader for me. He's just so iconic, and he's pretty cool, too. And he has one of the most remembered lines in cinematic history (You all know the one), and is overall a really great villain.

He one of my favorite character in Star Wars

Sauron is arguably the perfect "intelligent schemer" villain, at least post-Simillarion.

He also practically birthed the concept of the evil overlord as it exists in modern fantasy.

Vader has the greatest story arc from Sith to Jedi. He was truly honourable!