Only one game... series.

I would say Skyrim or an MMO because theyre heavily mod-able and neverdending, but going with Final Fantasy as the diversity of story and level grinding are all different game to game. There's a lot of spin off games I haven't even touched yet and a few of the older ones I haven't played. It will take me eons to beat Monster Arena in FFX anyway. Still going ;___;

Final Fantasy. Too easy.

1. FFXI + FFXIV = Social Interaction. Not only for basic gameplay but now this also includes Triple Triad and Chocobo Racing, as of... well, tomorrow, I think. There is also the added bonus of these games still getting updates, and FFXIV will probably be getting updates for a long time to come.
2. The other games will allow me to keep my sanity because I really prefer single player games to MMOs.
3. There is a variety in the other games - not simply RPG stuff, but also FPS and tactical games, which will allow me to get a bit more variety in my gaming than most other series would allow. Only Mario, if anything, might be able to beat FF in this regard. Not sure as I've played very few Mario games.
4. Potential for more games to come out in the series that aren't just the same games as before with a new storyline. That is a massive bonus.

This is the meanest thing somebody has done to me.