To answer the original question my favorite would be Robert Culp. He was great in Double Exposure(my favorite)and Death Lands A Hand. He did what he could in the Most Crucial Game which was a weaker episode.
Jack Cassidy is good but I don't know he seems to just be playing Jack Cassidy sometimes. Two of his roles are almost identical(Murder by the Book & Publish or Perish) but Now You See Him was his best to me. He did a good job in that. He's the 2nd best of the three.
Patrick McGoohan is good but hes a bit eccentric to me. He was very good in By Dawns Early Light (emmy nomination) but I didn't like him in Identity Crisis too much.(a bit weird)3rd.

Some other favorite villians of mine would be: Roddy McDowall, William Shatner, Ricardo Montalban, John Cassavetes,Trish Van Devere(favorite female) ,Donald Pleasance,Clive Revill, Martin Landau, & Robert Vaughn.