User blog comment:James12708/Reapers VS. Forerunners VS. Angels from Darksiders VS. Humanity from Halo VS. Council and humanity from Mass Effect VS. Imperium of Man/@comment-4967682-20130116065115/@comment-1683193-20130116140402

The Covenant seem to be somewhat superior to the Reapers. I'd say the Council would beat pre-war UNSC(although it would be a hard fight) but lose to post-war UNSC.