See title. The scenario is simple: you can choose any exclusive game from another current-gen system to be ported to one of yours. Any game. With some exceptions, to keep this grounded in reality.
1. Third-party games only. This includes "second party" games where the publisher doesn't own the rights to the license - so you could say you want Gears of War on the PS3, but you can't say you would take Halo.
2. Don't worry about power requirements. You want Gears on your Wii? Sure thing. You want Dissidia on your 360? You can have that too.
3. You can only pick games that actually exist.
4. Don't come in here just to say "well certainly not [game] or any of [platform]'s games" or I will report you for trolling. This is a topic where we express jealousy, not how to be jerks.
I think if I had to pick just one?
What can I say? I want to play this on my 360 something fierce.