We are unusually blessed in the Supernatural fandom with a cast that go out of their way for us, that seem to get along well and respect each other and that are generally pretty decent people.
Every report that you read or hear seems to point to a total lack of divas or assholes among them.
So, picking a favourite cast member is very difficult, in fact it seems a little unfair.
Therefore, I'm going to go for a purely shallow choice here. Nothing to do with who's the nicer person or the better actor. Just ...