Ruby
And you should probably be thanking me for that one, look what happened to Azazel in the end, to Lilith, to good old Al. All thoroughly Winchester'd. In the face.
Oh, I completely understand why you want it. Power is intoxicating. We crave it, you and I.
I just think it'll cost you too much in the long run. You think Sam will ever look at you the same way again? Think he'll be able to see you and not see them?