Well I misclicked; I voted warrior but meant mage. Anyways Mage is my favorite; but that does not think it is easiest; just most fun 'cause I like casting spells and with mages I can cast twice as many
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I think (for me) it is a toss up as to whether paladin or warriros are easier at the end of the game (mages are easier at the very start when you have fireball and flaming arrow against small stacks).
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I'm in the middle of my second game of warrior on impossible; and at leavel 18 I've breezed through the two easy sections of elves; finished dwarves and double trouble. My expectation is as I level warrior gets easier and by the end of the game well it will be fairly easy. With mage on impossible I always struggle a lot near the end (though that last fight is pretty easy when I go nuclear.