The Coolest

[Selmo]

I'm not quite sure what you mean by coolest.

The Witch-king was, indeed, a powerful character but he wasn't very successful.
He built a kingdom in Angmar only to have it utterly destroyed.
He failed in his mission to find Baggins and take the Ring.
He backed down from Gandalf just because he heard the sound of horns blowing.
His army was beaten by a much smaller force on the Pellenor Field.
He was finished off by a four-foot tall midget and a woman.

He doesn't seem all that cool to me.
.