I mainly play as Necropolis or Tower, generally choosing mages, but my principle is this: if I'm leveling up a mage:
- Earth
- Wisdom
- Intelligence
- Magic
- Water
and if it's a warrior:
- Leadership
- Luck
- Attack
- Defense.
And in general, I wouldn't refuse Pathfinding, Logistics, or Diplomacy if the map is large; if it's small, then you need to see what to take...
By the way, most people level up only one main hero, but I try to level up two main ones: one mage and one warrior.
P.S. I always take Property for all secondary hero-assistants, whether it's for resources