Even if I respect all the actor's efforts, I simply HAVE to pick Madsen.
Like someone else said, after RD, Michael will NEVER be some other character to me... he's born to play Mr. Blonde, similar to Brando being Vito Corleone. I believe it's really hard to portrait a character that far away from your own, personal character and still do a fantastic job at it. From what I heard, Madsen felt very uncomfortable doing the whole torture scence... but do you actually notice that? No, not a second, that's how well Michael plays that person. In my opinion, that deserves credit.