I would definitely go with QS. After he 'let go', he seemed to transcend the story itself to a degree -- at the very least he gained higher-dimensional status.
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yeah that's true, but that doesn't always translate to direct 'power' if you know what i mean. be interesting to see if qs could put atom down, and just what atom's energies could do to someone like qs...
In QS's case, I think it *does* translate to power, tbh.
If we look at Superman Beyond, QS had evolved beyond the concept of 'conflict' entirely -- it seemed as though he was immune to harm/damage all together. That's why Ultraman's HV just brushed off him, for example(and remember: Ultraman was written EXTREMELY uber in that series, as he lifted the infinite book SOLO.) So yeah...
QS also took the essences/ideas/concepts of Superman and Ultraman(ie. opposing ideologies), combined said dualities into a symmetry, and broadcast this pure, amalgamated essence straight into a 'receiver'(ie. Thought-Robot) in a higher dimension/Nil... Had it not been for QS, the heroes could have never even 'powered-on' Thought-Robot to fight Mandrakk in the first place.
And based on his [albeit brief] appearance in Pax Americana, we know time is an open book to QS as well -- a book he can fully perceive/comprehend, AND move through... So even the proverbial 'silver bullet' that wins DCnU CA most forum battles(ie. his temporal abilities) would count for nothing against QS.
Suffice to say: I personally believe QS is one of the most powerful beings in DC across the board.