I chose Clark. I don't really like the way he looks as Superman - I don't like the hair, and I don't even really care much for the suit.
Like Labrat, my real favorite it Clark without glasses - and for the same reason.
But, as BrightFeather rightfully points out, there's no getting around the fact that it's still Dean! He looks good all the time. Off hand, I can think of three times in particular when he just took my breath away. Interestingly enough, each one is a different "look":
Clark - when he was on his knees telling Lois "marry me". (end of Krypton arc, I forget the episode name)
Superman - when he kissed Lois' hand in Contact
Clark w/out glasses - when he came down the stairs and took off his glasses in Sex, Lies & Videotape.
- Vicki