Tactics. It does most things better than any other Final Fantasy. And Charge time with area of effect spells and job points is a great system.
FF I
FF II
FF III
FF IV
FF V
FFVI
FFVII
FFVIII
FF IX
FF X
FF XI
FF XII
FF Tactics
FF Tactics Advance
FF Crystal Chronicles
Other Spin-offs... (Dirge of Cerebus, Mystic Quest, etc)