From Wonder King Online Wiki

Pure Offense Builds:

Thief+: Luck

Scout+: Luck

Swordsman+: Strength

Mage+: Intelligence

(Note: Dexterity will increase by itself every 4 or 5 levels, the same goes for any other stat)

Defense and Offense Builds:

Thief+: Luck & Dexterity

Scout+: Dexterity & Wisdom

Swordsman+: Strength & Vitality

Mage+: Intelligence & Wisdom