FF Tactics definitely. All those chibi folks with homicidal impulses.. The switching from job to job, mastering them..
Next would be FFVII, it just broke my heart! :cries: Loved the soundtrack of that one.
FFVIII and FFIX would be a tie.. Different graphics, but the stories were just so.. COOL!
FFX, FFX-2 didn't really get to play them much.. But the graphics were just AWESOME... And am loving the AMVs done to them to bits.