Not enough is known on Prime to say on this.
They can both alter reality, cos Prime has his Sword of Truth and the last GL Ring, but can he match the manipulative power of Parrallax?
I don't think so to be honest...
And before mentions Supes' other powers, would they really count for much in this fight?
They should. I mean he can move 7.7 times light speed. I don't know how fast Parallax can move or anything but speed would be a good factor. And since he's been in the sun for 15,000 years I imagine his speed if even faster then that along with his strength, and he's already smart. If it was just ring against ring it be who had the stronger will.