The battle systems are the core engine for battles in the Final Fantasy series. This is a list of battle systems in main series (battle systems of Final Fantasy XI & XIV are not included because they are MMORPGs):

1. Traditional Turn-Based Battle system: Final Fantasy I, II & III (random encounter/battles; the player has complete control over the battle)
2. Active Time Battle (ATB) system: Final Fantasy IV, V, VI, VII, VIII, IX & X-2 (random encounter/battles; the player has complete control over the battle)
3. Conditional Turn-Based Battle (CTB) system: Final Fantasy X (random encounter/battles; the player has complete control over the battle)
4. Active Dimension Battle (ADB) system: Final Fantasy XII (field encounter/battles; the player controls the leader but can change the leader in the battle)
5. Command Synergy Battle (CSB) system: Final Fantasy XIII (field encounter/battles; the player controls only the leader in the battle) & XIII-2 (random encounter/battles with Mog Clock system; the player controls the leader but can change the leader in the battle)
6. Style-Change Active Time Battle (SATB) system: Lightning Returns: Final Fantasy XIII (random encounter/battles; the player controls only Lightning)
7. Active X Battle (AXB) system: Final Fantasy XV (field encounter/battles; the player controls only Noctis)

Which is your favorite? Do you prefer random encounter/battles or field encounter/battles? Which battle system do you want to see in the new Final Fantasy game?

My favorite is the ATB system and I prefer field encounter/battles. I would like if they return the old ATB system and improve it with a swapping system which allows you to use all the characters in the battle like in the CTB system. It should also be much faster and more active than older versions like in Final Fantasy X-2. They should also add co-op moves like in Final Fantasy XV. If they combine these elements with the ATB system, they could make the best battle system so far. They also need to return the battle system in which the player has complete control, without AI.