Why would you want to be someone rich? You guys realize it is for a day right? You can't really do that much in a day as a rich person that a moderately well off person can't do. Maybe a few truly extravagant things, but clear the answer is to be someone that you could never duplicate. Like a professional athlete, or whoever gets to fuck Meghan Foxx or whatever.
Who would rather be Warren Buffett for a day than Julio Jones? He's 80 years old. And even if you get brain damage as Julio, you switch back to yourself the next day anyway. Don't even gotta live with that...