I haven't done extensive testing, but I've been basing my play on the fact that D&D is an obvious inspiration, so -
Clerics have high Wisdom and probably low Dex. They're going to be able to heal themselves and may be better against Undead.
Wizards are going to have a high Int and be good at bursting down enemies, but their health is going to suck and their Str is probably comical.
Rogues are likely to have high Dex and moderate Int, Barbarians will have high Strength and Constitution, as will Fighters. Rangers probably have Good Dex and Wisdom.