As for Job class, Priest (sorry White Mage! :p), is naturally my favourite Job, although I usually mixed and matched Jobs with other Jobs’ abilities (Chemist with Float and White Magic, White Mage with Throw Item and Equip Gun, and most sword classes with 2 Swords and used the old weapon dupe trick to make enough Excaliburs, Chaos Blades, Save the Queens and Ragnaroks to equip every unit in my party twice over. :p)
I also like putting equip shields on the weaker classes like wizard and priest. It can be a real boon to keep them alive. I don’t like having that empty hand.
But Ninja, well, it’s all about Two-Swords. Sunken State and Abandon are pretty useful too, but having Two-Swords just makes any damage-dealing Job (especially sword-wielding unique characters with their own special Jobs, like Cid) so much stronger it’s almost criminal. Orlandu with Two Swords, Excalibur in one hand and Chaos Blade in the other = very dead enemies, very quickly. :p