This don't mean just villians either; or cool characters for that matter.
Like Cloud and Squall are purdy cool (if not half-emo each).
But folks like Auron and Sephiroth are truly badass. They'll kick asses, take names, and sleep with your wife as they do it. Hell Auron was badass enough to make Tidus (or as I call him, "He-who's-name-shall-not-be-spoken") ok to deal with. He was so badass, he had enough left over to put him into KH2!
So...obviously my vote goes for Auron. But your choices don't have to be FF or KH of course.
So, until someone else posts on this, stare in awe of his greatness' badassery:
https://www.youtube.com/watch?v=r6ZjHmNiAEw