There really isn't a difference in the core battle system mechanics from the original NES games until 10.
12 is the first major departure, 13 was a variation of the previous core systems, 15 is the move to action oriented gameplay and 16 fully embraced action. Remake to me has a lot of similarities to 15.
I think 12 is the most unique of the games in away. Its pretty much an off-line MMO but none of the other mainline games play like it. If you including non-mainline games than its Tactics clearly.
Tactics
12
Remake
in order for me.
I feel like rating the progression/side systems is a more interesting conversation.