I dropped my last char because it had all masteries

I'm getting new one nuker and trying to do little to no mistakes, 7 Fire and Pacheon now (farming).
I'm thinking about 80 Cold-Light-Fire nuker, though I have no idea should I get 60 Heuksal for extra HP, or 60 Force for extra MP and debuffs (Vital series?)
Someone said "The best defence is good offense." So? HP or MP?
P.S.
I'm saying this in advance.
I know I will die alot as a Full Force and I'm ready to die.