Oronar Skirata
I usually stick with the party that gets me through an area without dying and that allows for optimal strategy based on my skills. Of course with me unlocking classes it changes.
My primary setup is usually something like two knights/monks(or Ramza), one Black Mage, one White mage, one summoner, and a physical ranged character(Archer, Chemist with Guns, et cetera)
That sounds like a lot of management but it leaves a lot of options open, and probably makes battles pretty interesting. My last play through I had 5 male Lancers(dragoons) because I love the male armor and it's incredible simplicity, I think I gave them all double hand and or some quicken passive from a time mage skill? So they could jump really fast.
Oronar Skirata
In the tactic advanced games I can't say I ever relied too heavily on anything though having to change my character classes often. I can't even recall who I primarily used other than that Red Mage Viera you get for completing a quest.
I always use a red mage or two in the advance games, and have recently come to love Blue Mages to deqath, although they take a lot of preparation to master, especially when you have 2-3 of them.
last TA2 playthrough:
Main: Blue mage/paravir dual wielding holy absorbing katana's
2 human characters doing the same as main. Mastered almost all skills and used some dodge counter thing.
2 red mage/summoners with holy absorbing robes and ice absorbing shields with blood magic.
Sometimes I'd use a Gria with ultima shot, wanted a party of 5 Gria but their classes were very limited, and you get them so late in the game. Still torked they didn't make an MMO using all these races.
last Advance playthough:
Main character and human blue mage duel weilders.
Two red mage summoners
An Illusionist.