Dual at lvl.12 the extra fighter bonus and the extra berserk bonus are worth it, especially if you are playing with Exp. Cap off (download it on the IronWorks 'cheat' page-IMO this is not really a cheat
).
As to your quests go ahead and finish Nalias Quest, it is pretty easy and will give you some extra items and some good Exp.Seeing as you have 2 spare slots in your group you may as well go and get Keldorn and then proceed to Nalias home.
BTW, Keldorn really needs the gauntlets of dexterity to properly make him the force that he can be-I think these can also be found in the Sewers though you may have to get into a fight to get them.
Good luck with your game BTW.