I've never liked Archers. Knights are so-so in MM6. But they do stay useful because of their hit points. But MM6 is so tilted to Magic, that Archery looses its edge around L20. After that, Bows are just for not wasting magic on weaker foes.

Have someone focus on water magic early so you get the useful travelling spells and earn some extra money by enchanting items.

Getting access to the Meteor Shower (fire) spell as early as possible is smart too. It takes care of most of the enemies outdoors.

Fly (air) is also a very useful spell to get as early as possible.