Okay, now this is gonna sound weird... but... I'd prefer to play Ocarina over GTA4.
BUT....
If I could only bring one game to the moon, I'd bring GTA4. In that case, replay value would be the only deciding factor.
If it wasn't just those 2 games though, I'd have to take Ancient Domains of Mystery. It's a roguelike I've been playing off and on for about 10 years, and I still haven't beaten it. I could play it and nothing else for the rest of my life.