i only play on impossible
furthermore
paladin>warrior>mage
paladin why? he can acces to skills very early and possibly the only character who can max LEVEL and all his skills(not kidding)
paladin will have trouble during end beginning game turning into mid game(due to lack of good skills but after that it's just PLAIN steamroll for paladin) at least my experience
with the warrior his leadership is so very high that u can easily max out any army and use ressurect/gift to get units back and your units can kill easy with order on level 3
(max bless FTW)
and mage the only decent and this guy is that his upgrades from spells are really cheap(the higher magic skill is nice) but can't compete vs the mass skills from pala or the high initiave a warrior gets(which can oblerate your troops before even getting u to cast spells)(since 9 out of 10 times the warrior will be faster and can use strong melee unit to HARASS your troops
just my 2 cents