This is reeallly hard.... Considering there are soo many Perfect worlds out there........
Hmm...
But finally made up my mind andd... I shall go with Destiny.
Having your own gear, Armour, and weapons sounds quite interesting, no?
and being able to soar through different planets? My god that's good.
then again, really, I might choose other games depending on the mood
Like Herthes said, Mirror's Edge and maybe Portal would be cool. I'd also want to add "Remember Me" the game. The game is placed in a futuristic Paris and has some kind of a Coruscant look from Star Wars. It's an era where the most valuable things are your memories and some evil enterprise tries to take them away from you. There, you play as a "memory hunter". It's a pretty good game, I enjoyed it a lot. If you haven't seen it before definitely check it out!
I would definetely like to live on Skyrim.... it would just be legendary! With the dragons, quests, and that little Arrow in the Knee every soldier says, I wouldn';t even sleep at night! Maybe live on Bioshock, before everything turned into shit.