FF BATTLES WHO WOULD WIN,

[Lithera]

XIV Bahamut would destroy the others. He's at least 10x the size of any previous Bahamut. XIV BAhamut would be better matched against Sin (X) or Eden (VIII)

[Yamimarik]

XIV Bahamut would destroy the others. He's at least 10x the size of any previous Bahamut. XIV BAhamut would be better matched against Sin (X) or Eden (VIII)

It's not always about the size, but how you use it

[Gralna]

XIV Bahamut would destroy the others. He's at least 10x the size of any previous Bahamut. XIV BAhamut would be better matched against Sin (X) or Eden (VIII)

I'd say Bahamut Zero from VII is bigger than XIV Bahamut, although it's tough to gauge his actual size since he's only seen in space with no way to accurately measure how far away he is from earth to give a frame of reference to his size.