Have Squall, Zell and Rinoa

Squall: Attack, Magic, Recover, item
Zell: Attack, Magic, Defend, item
Rinoa: Attck, Magic, GF, Revive

All characters had around 255 VIT and SPR. This made Omega's attacks except for gravija and Medigo Flame do around 60 on physical and 30 for meteor(each hit) and for terra break around 300 per hit. Squall and Zell shoud have 255 STR and Rinoa have over 200 MAG. These stats can be obtained through using the STR+Bonus e.t.c when levelling up then junctioning the +60% stats.(ALL CHARACTERS SHOULD HAVE TRIPLE OR HASTE JUNCTIONED TO SPD)

When the battle starts have Rinoa cast Meltdown, Zell Cast Aura on Rinoa, and Squall cast Aura on himself. Keep Rinoa's command box up with the Limit arrow shown and as soon as Omega casts Medigo Flame use Angelo and pray for Invincible moon. Then use Zell's limit break Duel and keep doing booya and punch rush which with STR 255 do around 100,000+ in total(i think) get Squall to do Renzokuken and hope for Lion Heart. Also use Rinoa's limit break if you know how to use Wishing Star. When the moon technique runs out cast Rinoa's Angelo again and if a character dies quickly use revive or full-life. ALSO if all your characters get K.O'd hold R1, R2, L1, L2 because i think this helps Angelo come and revive you thats what happened to me and thats the time i won against Omega Weapon. Use a Pheonix Pinion at the start of battle if you have time so if you get K.O'd and hold the above Pheonix might come to your aid.