I much prefer having a character with higher MA values than a Ninja (Summoners are a great choice for this, as are Chemists with a Wizard's Magic Attack Up ability), with the Calculator's Math Skill, are a great choice for magic users. I discovered the joy of Calculators about three or four playthroughs ago, and now my favorite party is Ramza, Agrias, Beowulf and two player characters, a fighter (a ninja with the Archer's Concentrate ability works exceedingly well) and a magic user (a high-MA class with Math Skill, as described above). I don't like using Orlandu, he's too broken. With this party (especially with my using Ramza as a Paladin, i.e. White Magic as his other ability, Agrias as a Time Magic-wielding knight, and Beowulf and the ninja as Item-users), I can take care of damned near anything.
Goddamn, Calculators are fun. Well, the class itself sucks (that extremely low speed is...gah), but that Math Skill...so fun. I love exploiting the game's mechanics like that. Makes me feel like Red Mage from 8-bit Theatre.