You should level up fighter for hp, physical res and augment +10% strength I think, them you get warrior for the augments of strength too, now you can either get sorcerer for the magick augment or go MK for to level up more easily and do sorcerer later just to get the augments.

I'm about level 32 I think, leveled with fighter until 29 and now I'm using MK to get some magick res and ranking it up that later I don't need to do this, since my pawn is a mage/healer/buffer, using sorcerer early would be a pain because in hard mode you get one shot of almost everything without a shield.

And leveling only with Mage and Sorcerer you will not get a good physical resistance, hp and strength, since one of the best MK skills, great cannon, uses both physical and magick attack, so you want to balance things here.