Quote Originally Posted by Poetically Pathetic View Post
(erm...though I should mention I was already lv.100 with high-powered magic in Squall's junction list, equipped with Lionheart and Aura spells when I reached the end of the game... Ultimecia didn't last more than a couple of turns against me4.)
Even without that stuff she's too easy. In fact, being level 100 really wouldn't help any since she'll just level with you. The more important part is having good junctions. In which case you're better off using encounter none and using the draw points hidden on the island closest to heaven and hell rather than levelling.

As far as FFVIII bosses that gave me trouble. The only one that really comes to mind is Omega, and only because I lacked the abilities necessary to actually survive when I fought him the first few times.