Yoshimo is kickass until you get to Imoen. Valygar is over-rated. Minsc blows Keldorn out of the water, if only for his personality (IMHO).
If you're picking these just because you haven't used them before, well, it looks like you would balance this party out with a cleric/mage, straight mage, or (my fav....a MONK!)
Sorry had to add the monk for some fun. I do love the whole monk idea though. I'm gonna play one next time.