Who would win? I’d lean towards Spectre
Manhattan is extremely powerful but the Spectre is basically a god.
It depends, we havnt ever really seen Spectre cut loose and do whatever he wants. Because he is the Vengeance of God he has purpose and rules. Manhattan does whatever he feels like. And we know he has the power to destroy and create universes. I feel like Manhattan would win just cause he is quantum power, which is limitless, within the constraints of the Multiverse. I.e. there is only one Manhattan because he is so powerful. There are alternate universe versions of Spectre. So his power is clearly limited to his own universe. Manhattan is Multiversal scale being. Spectre isnt. So id say Manhattan