FFX, is not only my favorite FF by a mile, it is my second favorite game in existence, topped onl by Lunar: Silver Star Story Complete.
I recently replayed FFVII and enjoyed it although I am not certain as to which I would rank higher between VII and VIII.
I hated XII, because Vaan was a piss poor main character that could have been removed from the entire game and nothing would need to be altered; alongside Penalo however I liked her for some reason. My gripe with XII was it had so much story developmental potential, the setting was intriguing, the characters all interested save the aforementioned two and a jaw droppingly gorgeous game world, however all this was cast to the wayside because there is practically no development whatsoever and Vaan is constantly told by the bloody game itself he is a loser and should not be the main character.
It amounted to nothing more then a dungeon crawler and cheap MMO knock off in my opinion.