I've been into Supernatural ever since it started airing, in 2005. My favorite character is and has always been Dean; he is bad ass, hilarious and has such a complexity despite his usual frivolous behavior that is fascinating. I also love Cas and really like Crowley. Oh, and Death is awesome, he looks creepily funny while eating pizza.
My Supernatural OTP is Dean/Cas/Dean. The first seasons are really fun with its episodic nature but my most favorite season was the forth, I think, with all the Hell business, the pain and the hurt, Dean's 'recuperation', the introduction of Cas and the other angels... And I love to death the episode where Dean first puts his torture skills to use on Alastair, it was really intense. Talking about Alastair, he was brilliant, he shouldn't have been killed so soon but oh well.