IMHO.

Action based leans to a more fast paced game where action is itself a selling point, though if you try to impress with i.e. story and action is only a minor selling point, one should use turn-based system. It's all about the style of the game.

FF uses turn based because it matches the game style. Fallout uses the system because it works to that game style.

I would also invite you to look at Grandia. It has a turn based system that I absolutely love.

Then there's the question whether you will use "battle scene" where the player is transferred to different place and fights there, or if simply a battle mode is enabled (like in Chrono Trigger).

I would play it anyways as long as the battle mode does not intefere with the game style and mechanics like a hammer to the face.