Three of DC's extremely heavy hitters vs three of the Ivory Kings, the beings that killed the Living Tribunal and most of the abtracts and the Celestials. Fight is in a neutral universe. Spectre is fully backed. Who wins? Let them fight!
Edit: it seems that fully backed Spectre could be considered omnipotent, if so then we'll use the second most powerful version in the comics not fully backed which might be DOV Spectre or is it COIE Spectre? Do correct me if I'm wrong :-P