I think Vader became definitive. At face value he's cliche, but when you get down to it, he's a really complex character. An evil cyborg that still has a spark of good, always fighting on the outside, as well as himself internally.
Palpatine to me is more of an all-around joke than anything. Vader gets spoofed all the time also, but at the end of the day, people take him a lot more seriously as a villain.