Look at each ones Stats:
FFIV:
Description: Mechanic with a beard.
Weapon of Choice: Hammer
Special Ability: Peep (scan)
FFV: (not playable)
Description: Crystal Engineer with guilt issues
Weapon of Choice: Wrench
Special Ability: Engineering (he retrofits the Airship and unlocked Crystal draining tech, what more do you want)
FFVI:
Description: Beared man in a yellow slicker
Weapon of Choice: Magitek Armour
Special Ability: goram Magitek!
FFVII:
Decription: Chain smokin middle aged southerner
Weapon of Choice: Polearm
Special Ability: Highwind Limit Break
FFVIII:
Description: Rotund headmaster
Weapon of Choice: SeeDs
Special Ability: Sleeps with Edea (cause there's no other way that would happen under normal circumstances)
FFIX:
Description: Oglop (or King-post Oglop status)
Weapon of Choice: Hildagarde Airship
Special Ability: bug like status (or pimping post Oglop status
FFX:
Description: Bald Al Bhed
Weapon of Choice: Presumably a Gun
Special Ability: Engineering (like Rikku's Steal ability)
FFXI:
Description: Slightly portly 10day stuble engineer
Weapon of Choice: Gun if not Hammer
Special Ability: Political Power
FFXII:
Sorry no spoilers for those that haven't played it yet.
FFT:
Description: Middle-aged man in armour and a hood.
Weapon of Choice: Excalibur
Special Ability: EVERY SWORD ABILITY!
FFIV tries to hide and use peep to spot the enemies weakness
FFVI aims the cannon of his Magitek Armour and fires, killing FFV and FFVIII (who is busy trying to convince Squall not to be emo)
FFVII, FFIX, FFX engage in an aerial battle. FFVII wins do to the Massive amount of missles and the lack of on FFIX's or FFX's. FFX only having Harpoons.
FFT uses Bloodsword to drain HP from FFIV and kills him slowly.
FFVI fires upon FFT, who uses Jump ability (gained from Lancer 2400 JP) followed by Armour Break x2 (Two-Sword gained from Ninja 900 JP)
FFVII enleashes Highwind
FFT uses Teleport (gained from Time Mage 600 JP)
FFT wins