FFVII is my favorite with VI as a close runner up. Both had great casts of characters, involving plots (even if VII got a bit confusing around the third act), and kept their character management systems simple and uncluttered. VI's was hugely diverse and had their own thing going on. Plus the open-world freedom of the World of Ruin was a nice change of pace. The Esper and Materia systems were simple and intuitive in character growth and flexibility. Admittedly though I just used the same characters near the end (usually the ones whose Limit Breaks/special skills I liked the most).
Which leads me to why VIII and XII are the ones I can't stand. VIII was badly written and had by far the WORST protagonist (and arguably the worst cast) in the entire history of the series as Squall had absolutely no justification for acting like an unlikeable, cooler-than-thou jerk. XII's problem was that the characters had nothing to them. Even the ones that had potential fell flat due to lack of development and most of the story problems (slipshod narrative and flowery dialogue) I attribute to the game only being half-done. And don't even get me started on the character customization. The Junction system in VIII was a test in how much you liked staring at numbers and engaging in busywork that insures that you will never, ever want to cast magic. Plus you could break the game by just spamming GF's over and over again with no significant penalty. XII was also a cluttered mess. The Gambit system COULD work, but when the fighting is turn-based in what is essentially a real-time environment it HURLED me out of the game at terminal velocity. That and the summons and Limit Breaks were useless and overpowered (sometimes) respectively.
