I'd place a "classic" Source above the Anti-Montor, as it was essential Jack Kirby/the 4th World's image of God.
As recently as DotNG, however, the Source was turned into a piece of shit (and that's unfortunately the most canon version). The Source lacked omniscient and omnipotence (two classic characteristics), was said to be forcibly split in half against its will, and generally lacked intelligence of any kind.
That Soulfire Darkseid was essentially the Source's equal in that story is impressive indeed, but probably not enough to overcome COIE AM, IMO