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I'd choose Imoen. Dualled to a mage means she can cover thieving and magic duty. (You don't really need a mage until later on anyway, and with two party members you'll be dualling her quite early).

For the PC you need fighting, and you'd like healing. the C/R already mentioned is a decent choice, a straight paladin might do well too. Other choices might be a dwarven or gnomish F/C (as already mentioned you're really going to want good saving throws). A fighter (or ranger) dualled to cleric might be a very good choice too.

I did the whole game with two self made characters, a fighter dualled to illusionist, and a thief dualled to fighter. Only fight that gave me big problems was the final one, and I only beat that by being very cheesy.