I gotta agree with the "certain Gf's Match certain people" but my list is so far off it's ridiculous. I don't know WHY i assume they fit, but somehow they...do? i dunno.

Squall was ALWAYS with Shiva (and Diablos). ALWAYS. He got Bahamut towards the end of the game ninety nine percent of the time too.

Quistis ALWAYS had Quizacotl, and Siren

Rinoa was usually with Leviathin (and brothers, who i thought fit's zell more, but it was a strategy thing. hp +80% holla)

Zell got Ifrit. Not a bone in my body allows thte thought of him with another person, like Shiva and Squall.

Irvine got Alexander and Eden. Big Firepower just seemed to fit.

Selphie.... Selphie was my oddball one. Obviously she gets Carbunkel, hyper little green gerbil. the odd thing is... Somehow, when the Evil lookin Big hitters like Bahamut and Eden weren't attached to someone else.... they just went to her (along with doomtrain). Maybe it was just the irony of the "selphie the little girl likes to play HARDBALL" Then there was the whole thing with her and Ragnarok that just reinforced the "Selphie and Big Evil Dragony Things with Lasers"

And Edea and the tonberry king. lol