It would be definitely mage. Warriors can only use their weapons at close distance, and assassins must remain undetected to do their job effectively. Mages can do so many things, for example use lightning, fire and frost to fight, control minds of enemies, become invisible, turn iron into gold, breathe underwater, levitate objects, raise undead, light dark caves and heal themselves and their followers.
Mages don't need to carry other weapons, because they can just summon bound bow, dagger, sword or battleaxe if needed.
Other thing is when arrested, guards take away weapons of warriors and assassins, but they can never take arcane knowlegde and wisdom, weapon of wizard.