I give all Power Ups to Sora. My strategy for the timed colliseum tournaments is to use Thunder magic as much as possible, and more MP always helps. The Spellbinder gives Sora more MP but is weak, so he need Power Ups to counter that. AP Ups I spread out between Sora and Goofy, because my Donald is only ever short on AP by 1 point, and he doesn't really need Berserk all that much. Defense Ups I spread between Sora and Donald, depending on who has the lowest defense at the time.