It depends... if it is a scenario where ALL games in the world will be destroyed except for the ones I pick, then:
1. Minecraft
2. The Orange Box (For TF2)
3. An MMO (I've never played one so not sure what to pick. This is also assuming there are no subscription fees, although we'd probably have to pay more given that it is one of 3 games in existence
)
If my decision only affects me, then I'd take Skyrim/Oblivion instead of the MMO.