[Sailor Steve]

That would be the afore-mentioned Master. The latest version, the one you mention, was written as a little to insane for my taste. Personally I don't think any of them have come close to the sinister but mostly sane original, Roger Delgado. I find it highly entertaining that The Master, considered The Doctor's archenemy, didn't make his first appearance until Season 8.

My favorite villain? I don't have one. Some are better done than others, but they are what give the stories their impetus. Without villains there could be no heroes. I voted for the Daleks. I didn't like what they did in the return of the Weeping Angels, but their first appearance, 'Blink', gets my vote as the single most entertaining and original episode ever.

@ JU_88: The "How old are you?" thing doesn't work with me in this case. Paraphrasing Will Rogers, I like to say "I've never watched a Doctor I didn't like". William Hartnell doesn't predate me, but I didn't see a single one of his shows until long after he died. I loved Tom Baker, but I also love David Tennant and Matt Smith. As long as the shows are well-written (I won't say well-done) I like them for the stories.