I thought II's was great if you know what you're doing.

To me the most enjoyable was a tie between IX and X. X you're looking right at the sphere grid and want to get that next sphere. IX you're always gaining new abilities, and always reconsidering your strategy on how to customize your character within his/her job class(es).

I thought Tactics was tedious as I basically tried to get every ability for a job in one battle when leveling-up outside of the story.