Later on I prefer to have every character assigned specific GFs and elements. So Quistis would get the holy GF, Squall the Fire GF, etc. You're right I think, that the beginning GF pair are pretty good, although I would make Quazequatil his own group because he has 3 spots to fill in the stats already. Maybe Diablos too, because at that point in the game only Diablos and Brothers have HP additions (i.e. HP+20%, HP+40%, HP+80%) and in the beginning HP is EVERYTHING.

Keep in mind: watch your Spirit stats. This is, after all, a war against the sorceresses.