Have played some of: FFII, FFIII, FFIV, FFIX, FFXI (3 months in 2008 or so, level 40 PLD or something), FFXIV (Loony Bob, Lindblum)
Have played over 50% of: FFI (currently playing), FFVI
Have beaten: FFV, FFVII, FFVIII, FFX, FFXII, FFXIII
Spinoffs: Seen Advent Children, seen The Spirits Within, finished VII: Crisis Core, played some of Tactics Advance (50%? Not sure!).
Own: FFI, FFII, FFVII, FFVII:CC, FFVII:DoC, FFVII:AC, FFVIII, FFIX, FFX, FFXI, FFXII, FFXIII, FFXIV, FF:TSW.
Favourite overall game so far? Still FFVII for the all-round package of backstory, characters, story and the fact that the story actually changes depending on what you do, Shinra/Turks/SOLDIER, sidequests/minigames, materia/lifestream ideas, Sephiroth, etc. etc. It also wins on outright best story, outright best villians, outright best backstory.
Favourite job system? FFV. Special mention to FFXI.
Favourite sidequests/minigames? Three way tie between VII (Chocobos/Yuffie/etc), VIII (Triple Triad etc) and X (many minigames!).
Favourite group of playable characters? FFXIII. The depth given to these characters outdid the rest as far as I'm concerned. I adore the lore, too, as it offers so much potential. I look forward to finding out about more of the FNC universe.
Have I played/watched an FF I didn't enjoy? Not yet, although TSW was probably the biggest disappointment as it wasn't nearly as good as I'd hoped. Still watchable, though. Oh, and Yuna and Tidus were easily the most annoying characters I've ever had the displeasure of playing. If the FFX gameplay wasn't so good, I'd have put this down as a game I didn't enjoy.