hi. it can get tricky cant it?
i think though, that the best way is to look at who is in your group,one by one. i assume your chars are all self made other than imoen.
imoen, has pre-allotted proficiencies.
Q-staff, Shortbow, Dagger. i think it best to let her use a bow and a staff, or on level up prof-a longsword. eventually you will find the gesen bow, the tuigan bow or the tansheron bow, these weapons - which is usually the best for her, with a elemental summonning staff like the fire one from the planar sphere.
cleric. would usually need profs in sling, and mace (M.Of.Disruption+2) a very nasty weapon against undead. this way you can use armour and shield, keeping ac nice and low.
bard. long bow and spear (impaler+10 in underdark is Xcelent)then ixils spike in tob. or longsword.
fighter one. Xbow(**) and two handed sword.(****)
fighter two. long bow(**) and halberd. (****)
this may worry you for a bit as halberds are hard to find early on. but the wave, the duskblade and others are a little further in but worth the trouble.
as you level up, give one fighter profs in flail and the other one in axes.
for your mage, quarterstaff and either darts or sling. you wont run out of bullets for sling easily, but darts have some good effects, like poison.
there are stacks around, if you dont mind carrying a few bundles.. your other option is a returning throwing dagger like the boomerang dagger. of course you will want to use the staff of the magi from the twisted rune.. or a summoning staff like the staff of earth. your ranged weapon is really your choice.
hope this helps some
Cheers.