I gotta say it was Oblivion… Until I decided I wanted to start playing again yesterday, and some how when changing my gamertag name I lost a bunch of save files and I’m like 15 hours back from where I was… So yeah 
I don’t think I can replay all that shit…
Otherwise I’d have to say I put over 40-45 days of my life into World of Warcraft, and I mean 24 hours times 45… so yeah, I’d have to put that as my favorite game.
I want to find a new MMORPG to play. That my computer can handle… WoW’s had to many patches and expansions and has another expansion being made, so my PC just can’t handle it any more lol.