When distributing AP, you want to put all of your points into your primary stat. Even though putting points into Crit may increase your attack number, your actual DPS from putting all of the points into your primary stat will be higher.
Strength (STR): Berserker, Knight
Dexterity (DEX): Archer, Heavy Gunner
Intelligence (INT): Priest, Wizard
Luck (LUK): Assassin, Thief