definately the fighter/mage. you get them to a high level, and they just kick ass. you can nail enemies with magic before you close for melee. and who wouldntt run from a fighter with strength cast on him, with a stoneskin spell. so IF you get hit, it will do NOTHING for a few hits, giving you SO man advantages. also, a thief to 11th level, then dual to a fighter, that kicks butt too. get to 12th level, and a thaco of 9, you get all specialization bonuses, strength bonuses, and weapon bonuses, combined with the enemies -4 penalty to ac when you backstab, and you are doing ALOT of damage.
Just My Two Gold Pieces
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Morgan Corbesant, Elven BladeSinger, Captain of the army of the Seldarine