Hate to jump on the bandwagon, but I used to be a huge mmorpg fan, so SOA is right up at the top of the list for me.
However, there is one above it. Not any specific anime, but I think I'd most want to live in any typical slice of life-type highschool anime, even as just a background character. If you've ever seen Watamote, that's pretty much what my highschool experience was like...actually, that's pretty much what it's been like for me all while I was growing up.
That's probably why Angel Beats is my favorite anime. The chance to do it over, and to not regret. :3