I tended to keep my party combination relatively consistent between the two BG2 playthroughs I did.
I played SoA/ToB, heavily modded, with a party of Jaheira, Yoshimo (modded so he survives past Brynnlaw - love his sarcastic quotes), Xan (squadmate mod), Minsc and Imoen, usually switching the sixth between Valygar, Anomen or Keldorn. In ToB, Sarevok is always in the sixth spot no matter what, with Xan usually switched out for Keldorn.
It gives me the best mixture of everything the game has to offer. The best quotes come from Minsc (though annoying if you're a goody-two-shoes like I am), Jaheira (romanced) and Yoshi. For sneaking/cracking locks, Yoshi becomes a god in the last handful of chapters and ToB (especially in Watcher's Keep). For raw survivability and tanking, my PC (straight-out fighter), Keldorn and Sarevok can handle the workload.