i completed a 16.4 MB game app for my iPhone. Now i want the same game for the ipod Touch and iPad but i don't know whether it's better to make it a Universal device app on Xcode or just convert iphone to ipad seperately on xcode?

If i don't do Universal and do seperate files, could it mean if i upload them to app store at same time, one version may get rejected while the other approved?