User blog comment:ImperiexSeed/ARCHANGEL or LEVIATHAN!/@comment-4393153-20120520025657

Leviathans would probably win, since they can kill angels (as shown by Edgar and confirmned by Castiel). Archangels and angels, just stronger ones. As shown when Dean tried to use an angel' blade against Raphael, the regular angel blades are still deadly to them, they can also be trapped by holy fire. From this we can see that archangels have regular angels' weaknesses, ergo Leviathans can kill them. Similarly, leviathans can only be killed by either each other or the bone of a righteaous mortal dripped in the blood of the three fallen. The bone can only be used once and it drags anyone involved in killing the leviathan back to purgatory with it. So, I'd say that the leviathans would win