Secondary skills in Heroes 3.

If the hero is a Warrior (Castle, Swamp), then: Attack, Defense, Logistics, Pathfinding, Earth(!), Air, Artillery, Resistance. If the hero is a Mage (Tower, Rampart, Conflux), then: Wisdom, Earth, Air, Water, Fire, Intelligence, Pathfinding, Logistics. If the hero is a Battle Mage (Castle, Necropolis, Dungeon, Inferno), then: Leadership (Castle) / Necromancy (Necropolis) / Resistance (Dungeon) / Fire (Inferno), Earth, Air, Water, Intelligence, Pathfinding, Attack, Wisdom(!)

Pathfinding and logistics are necessary for all heroes, as is earth magic. IMHO.