I have to go with the archangel Zachariah. Castiel called them 'God's most fearsome warriors', and they'd have to pack some kind of celestial coup de poing to be called that! Since they've already established that Sam and Dean's destinies must be allowed to play out, we likely won't see just what he is capable of for a while. He will not interfere...yet.
(btw, this probably should have been a pick because it's an "opinion" question, ;) )