If u use a caster + sigil u get bonus M. Atk +5% by pasive skill but M. attack in a weapon 99 is 371 for caster and 408 for retributer. Sigil will give you 50 Pdef and mp recovery bonus 20% but using BTM and with a decent healer in your party, u can manage your MP well enough using a retributer.
I used caster + sigil till lvl 97, after that i changed to retributer.