Arguably? It's probably FF 2. Even if it pushed the story aspect of FF foward, it's combat system was a mess, and the constant switching betwenn party members just made it worse.
Personally? probably either FF 8 or 15.
My (locked) thread about how difficulty should be a decision for the developers, not the gamers.
https://gamrconnect.vgchartz.com/thread.php?id=241866&page=1