I always send Quistis and Selphie. I feel like I rotate between Zell and Irvine for the third party member, but it's usually Irvine.

I always think of my party in terms of an A Team and B Team, and I just do a junction exchange every time I switch between the two. I generally see Quistis as the leader in the absence of Squall as she has a little more experience in that area (not that anyone showcases good leadership a lot of the time). Rinoa and Selphie are more my magic type and they do the junction exchange. Irvine and Zell are the second set of damage dealers that I junction exchange between. Considering I play this game at least once year (last year being the first time I haven't), I'm surprised I've never sent Rinoa to the Missile Base. I should do that next time.