User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-63.117.245.61-20111228195502/@comment-5605779-20111229044612

Just to clear things up, Death does not "serve" God. He stated that he is more of an acquaintance to God. And as for who is more powerful, just look at the facts. God's abilities:

■Omnipotence: God is said to be the most powerful being in the universe, however it's unknown if he is more powerful than Death. ■Omniscience: God is said to have unlimited knowledge and awareness and understanding of the universe. Yet he doesn't know whom is older, himself or Death, as stated by Death. ■Omnipresence: God exists everywhere in the universe as he is one of the two fundamental forces in it, the other being Death. ■Immortality: God is older than time and also possibly even than Death, but neither remember who is older. In terms of immortality, he is invincible to all harm, as well as never aging. It is possible that he can die as Death said that he will reap him in the future. ■Teleportation: God was able to put Sam and Dean on a plane, when they were outside Lucifer's cage. ■Resurrection: God was able to resurrect Castiel.

Death also has those powers, but it was also stated that neither he or God knows who is older.