So, we jump from a question that is too easy, to a question that is far too hard.
Best scene ever in ANYTHING? Even if I just try to choose a best scene ever in Supernatural - that's impossible. I can't even pick a favorite episode, let alone a favorite scene!
How about we do it this way...
Jensen's Best Scene Ever: Extremely hard to choose - but I'm going to go for the soliloquy over Sam's dead body in AHBL2. Close runner up is arguing with himself in The End.
Jared's Best Scene Ever: I really like Samifer (I also really like Jared's Meg - it's ironically the only time I enjoyed that character)...I also love his big puppy eyes...anyway, I'm going to go with the mirror scene in Swan Song, because we get both Sam and Lucifer. Close runner up is Meg!Sam attacking Jo (I don't care what the feminists say, that scene was frickin' hot), and all of Mystery Spot.
Best Brotherhood Scene Ever: I absolutely love the scene in Playthings when Sam is drunk and clingy and adorable, and Dean is all exasperated. Seriously, how could Dean possibly promise to kill someone THAT adorable?
Best battle scene: Storming the Earth King's castle in Avatar: The Last Airbender.
Best sword fight: Inigo and the count in The Princess Bride.