Lord in heaven, how did I miss this thread?
I don't think I could possibly choose between Jared, Jensen, Tahmoh, Jamie Bamber, and Michael Trucco. And Justin Hartley. And Eric Johnson.
But then I enjoy group stuff, so that's fine with me.
BTW, did you know that Jensen wasn't even originally supposed to be in the show past the first episode? The show was pitched as "The Sam Winchester Show," and Dean was just supposed to set him on his way. It was only when they saw how well Jared & Jensen worked together that they retooled it into the brothers concept.