Wisdom
4th school of magic
Logistics
Intelligence
Diplomacy or Literacy

The last two skills are still a burden for the main hero.

It is wiser to choose Attack, Defense, or Archery (depending on the situation).

If the focus is on brute force, it is more reasonable to add Attack – it is still more important for the main hero to be able to defeat neutral creatures than to recruit troops (a secondary hero can handle the latter, and it is not necessary to level him up beyond the fifth or sixth level for effective operation)... Also, for a "brute force" hero, Pathfinding will be more preferable than Intelligence: speed, and again speed, is the best tactic for him...

If the focus is more on magic, Defense will be more effective. It is generally more effective than Attack and can only be inferior to it if you have the first turn. Defense also has an advantage over Attack if you have archers as the main core of your army. Attack does not help archers – the Archery skill is more important for them...

Special case: Air + Intelligence (if you have Fly or Dimension Door) will more than compensate for Logistics + Pathfinding. Here, everything depends on the terrain of the map and the ability to obtain the necessary spells. And all this is already visible at the start of the map, which allows you to make the right choice when upgrading the skill tree from the very beginning...