Yeah, so I almost feel like I made this topic just so I could procrastinate working on my 20-page-paper. Ick.
Anyway, of the FFs you've beaten, rank them from favorite to least favorite. Heck, add in Kingdom Hearts games too if you want. And the Chrono series. And Tactics and Crystal Chronicles if that floats your boat. Just remember that you're only ranking the ones that you've beaten.
Here's mine, from favorite to least favorite, though it's very hard for me to rank them. All I know is that Kingdom Hearts is my clear favorite, and DC is clearly crap...in my opinion:
KH
FF X
FF VII
Chrono Trigger
KH II
FF X-2
FF XII
FF VI
FF VII: CC
FF IV
FF I
KH: CoM
FF VII: DC