And whichever one you pick, you have access to the "powers" of that universe. For example, if you picked Star Wars you'd have a a Midi-chlorians count (lel) which means with training you'd be an expert jedi, if you picked Dragonball you'd have an easy time of using ki and train with master roshi and others to get stronger, hopefully you know wat I mean.
So which one?
I'd pick the DC Universe on Earth. Why? To chill with Batman of course. Or Star Wars, either one.
P.S You can also chose which period of time you can first enter the universe.
[Edited on 01.05.2013 7:33 AM PST]