Hmmm...
IV & VI: Can't really remember. I know that my favorite parties by end game were Cecil, Kain, Edge, Rosa and Rydia (obviously), and Celes, Locke, Edgar, Sabin, Cyan...I think.

VII: I never used anyone besides Cloud, Vincent, and Yuffie really. Well, before I had Yuffie I used Aerith, and before I had Vincent I think I used Barret...maybe.

VIII: Haven't played enough to have a strategy...I just know that I will always have Squall and Rinoa in my party. Yay couples!

X: By end game never really used Wakka...I also NEVER used Rikku or Kimahri.

XII: Fran and Balthier got the shaft for some reason.