I´d the same problem as you, specially when I was trying to have the best junction in order to defeat Omega, so if you wish, you could use my junction:

1. Squall
GF: shiva, diablos, pandemona, doomtrain, bahamut, eden

2. Rinoa
GF:Quetzacoatl, Siren, cerberus, alexander, cactuar

3. Irvine
GF: Ifrit, brothers, carbuncle, leviathan, tonberry

If you need an ability, select from the Item menu the Amnesia Greens (I think that´s the name... you can buy them at any pet shop) and then erase one of the GF abilities (like Magic, Draw or GF... all of them have these abilities) and then use one of the items in your menu that provides the GF with the ability you want to learn (ex. adamantine makes a GF learn Vit + 60%) Other rare items like three-stars (you get it when you defeat either Ultima or Omega Weapon) makes a Gf learn the Exp3x1 ability... so you just have to select whatever you wish your GF to learn and customize them.