What mixed hero class of the Haven faction do you like?

In reality, for balance, the Archmage only overlaps with its combination with Nature. But even here, you need to decide whether to invest in an additional school for the hero for the effect of +20% to all spells (and how many of them are there, besides summoning, for Haven? - those that are quantitatively enhanced).

All combinations of Haven with the other remaining magic schools give a completely different effect, not related to enhancing spells.