Pixie-fairies can fly, have high wisdom stats and aren't very physically strong, so the best classes for those would probably be...

Magician, Enchanter, Diabolist, Illusionist or White Wizard. I usually play the White Wizard role myself, and it's not very dangerous in terms of attack, so that shouldn't be a problem... I'd say Magician or Diabolist would probably be the most dangerous if leveled right. Magicians focus on magical damage, while Diabolists focus on summoning. For direct damage, Magicians are probably better. Diabolist is kind of a weak role early on, so leveling is a pain.