Repair is the king. Farmers, craftsmen, housekeepers, pretty much everyone has uses for it. Heal would be second as it's generally useful but not needed as often.
Others would tend to be more occupation-specific. Hunters, for instance, could use Mobility, Farsee, the missile spells, maybe Slow, etc. (And in Prax, of course, there's the Peaceful Cut, though that's more a skill than a spell.)