I'm hearing a lot of things echoing what I was thinking already. Jan and Haer'dalis are secondary casters for the most part (though in my 4 man shorty party Jan's doing okay), so an arcane could be good. And at the same time there are no real warriors either, though everyone but Jan has moderate combat abilities. I've actually never played as a Kensai>Mage, Sorcerer or Barbarian, so those are all appealing options... leaning toward Kensai>Mage... hmmm...
How about a shorty party with:
Korgan
Mazzy
Jan
I went Dwarf Fighter/Cleric, what would you guys have picked?