Like Greed said and like it says in the faq go all int until 20, then 3 into int and 1 into vit. Also choose fan because it gives you more Magic Attack.
Q: Isn't it better to max out Penetrator before DS because it hits more targets?
A: Well yes it hits more targets, but when maxed it only does 190% damage while DS does 330% damage. So you decide if you want to do 190% damage to 1-4 targets, or 330% to 1-2 targets.