User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-31.53.226.53-20120607165416

It can't really be confirmed which is stronger but i would guess leviathans on the basis they are immune to angelic powers and their black goo seems to be toxic to angels. also leviathans don't seem to be afraid or affected by archangels methods of torture as leviathan sam didn't really seemed bothered by sam's visions when he absorbed them, he just found it mildly irritating but castiel went completely insane when he absorbed them.