Limit Breaks are definitely the way to go. I remember I used to sacrifice Quistis at the very beginning of the battle with Kamikaze, so I would take Ultimecia on one hit. Then I would be using aura stones all the way after beatin them with Limit Breaks only. Also try to time the turns in which you know Griever is going to make a Shockwave Pulse and summon your GF's so they get killed instead of you.
The best limit break I was able to use was Irvine's, there were a couple of ammo (the most powerful 2 types) whcih names I forgot, I remember I'd deal the most damage with him, and with Rinoa's Wishing Star. I never got the Lionheart
