VI: Terra, Cyan, Setzer, Shadow, Relm, Strago, Mog, Gogo. Obviously I used them all a fair bit, but if I had a full allowance and only one party to create then it was generally made up from the rest.
VII: Barret, Cid, Yuffie, Aeris, Vincent, Cait Sith. Basically I always used Cloud/Tifa/Red where possible.
VIII: Irvine, Quistis, Selphie. They all got their turns, but not nearly as much as my preferred three.
XII: Penelo was my least used, but the others all got a lot of gametime. My preferred starting trio were - if I recall correctly - Ashe, Basche and either Vaan or Fran depending on the circumstances.
XIII: Fang, Hope and Snow earlier in the game, although I used Fang a lot near the end and Hope had his uses.

VII was definitely the game in which I rarely used 'subs', though. All the other games either have easy switching mid-battle, few characters to pick from or forced use of multiple parties - or a mix of the lot!