Devout - A Tanky upgrade White Mage, they get access to all the higher tier white magic spells. They are nerfed in the DS version having lower stats and spell charges for their magic.

Magus - Same deal as the Devout, a more robust Black Mage with access to all the endgame spells. The stat spread isn't quite as bad from the DS version. The NES version has lower strength but higher vitality. As with the Devout they have higher spell charge count for all of their magic.

Summoner - The is like the most tinkered with class. The NES version has slightly lower stats except for Vitality of which it has a huge drop off from the DS version. The NES version has lower spell charges as well but summons are pretty brutal. Summoners do the full summon showing off the signature attack of all their summons.

The main issue with the classes is that they are a lot like Internet Explorer. You'll use them once to help you get Sage and then they are all instantly obsolete. Granted, Eureka is no cakewalk, so thankfully these classes are good.

Sage is a beast of a class in this game and is the ultimate mage class. They can use any white, black, and summon spell in the game, and unlike their nerfed counterpart in the DS version, they use the full summon. Their overall stats are also better in the original making them fairly tanky, and they have the highest spell charges for all eight ranks of magic of any magic class. With three slots per level you can heavily customize them to your liking. Just remember that the Lv. 8 magic is in Eureka's shop and super expensive so choose wisely.

Ninja is the ultimate melee class in the game. They can equip any item that isn't the Onion Gear. They have the best melee stats on par with Black Belt but actually have real magic defense, so they can take better damage. They have no special ability but they can equip the rare Shuriken item that is super expensive in Eureka. Shuriken has the same attack power as the Onion Sword and when a Ninja uses it in battle, the weapon is lost since it was "thrown" so you'll need to equip a new one every round. I'd save them for CoD personally.