The question when it comes to level 51 is: where to distribute stat points?
Here are:
Strength : More Physical Damage (Close Combat) ; More Double Attack Rate ; More Critical Damage ; More Piercing Damage (Physical)
Agility : More Physical Damage (Distance Combat) ; More Critical Attack Rate ; More Hit Chance ; More Avoidance / Evasion Rate
Intelligence : More Magic Attack ; More Level of Heal ; Less Cooldown in Spells ; More Piercing Damage (Magical)
Luck : More MP ; More MP Regeneration ; More Resistance at Abnormal Status
Constitution : More HP ; More HP Regeneration ; More Resistance at Critical Attacks
Then,...
Warrior : Strength
Crusader : Constitution
Dual Gunner : Agility
Night Magician : Intelligence / Luck (i think that intelligence is better than luck)
Sniper : Agility
Cleric : Intelligence