Considering the aftermath in MM#15 I'd have to go w/ KM; however, this would be a great fight. Their both incredibly powerful and crazy as hell.
Superboy Prime wins easily.
To my knowledge, Kid Miricleman can lift several hundred (to maybe a couple of thousand) tonnes.
He can fly around at mach 2 (aaproximate).
His invulnerability is based off a forcefield close to his skin but he be ko'ed and hurt through this screen but it takes quite a lot of force to do so (getting on to a mini-nuke level to kill him).
He also seemed to have some energy projection (lightning based maybe).
Superboy P on the otherhand can lift trillions of tonnes (or more but enough to move planets).
He is invulnerability can easily withstand nukes.
He can fly faster than light speed and his reactions are close to those of the Flash.
Thats before we get to his heat vision.