Unless Darkseid can mindrape him, Prime likely wins.
"The Grand Admiral was smart and subtle, but never used his brilliance to show up or humiliate anyone.
He demanded results, but never perfection, and had amazing stores of patience for those who were truly working to their fullest ability.
It was a pity Thrawn's style of leadership hadn't spread through the rest of the navy.
If that happened, he suspected, the Empire would stand forever."
Prime. this version of him is too uber. darkseid is very cocky he will taunt prime, probably call him a child and say he is not worthy of his time. then Prime gets into his i kill you to death mode, heads will be shoved up asses, fun fun fun.