For me works well even on the highest difficulty level.
Town preferred: Dungeon, why?
- magic whirl (restores mana + mana x2)
- heroes from Dungeon learn mainly Power and Attack skill
Main hero: Gunnar (logistics - mobility is a key to success)
Tactic is quite typical and logical:
1. Visit enemy as fast as possible, or wait max.1-2 weeks. Waiting longer = sieging castle with towers. Sometimes, with a bit of luck and flair you can take off empty castle and wait in castle for opponent to attack you. Remember. Number of towns is essential (in WoG also experience)
2. Number of mines is important too, in second place. Don't waste time on picking materials, you can take them later by your other, lesser heroes.
3. First capitol, then army. But it isn't a rule. Sometimes it's better to faster take off more castles than build a capitol in one of them.
4. Develop towns which are nearest to the enemy (faster source of army).
5. Don't leave towns without a 'regent'. Use them to flag nearby mines.
6. When fighting use 'wait' button, it wasn't created just for fun. Use 'wait' to get to shooting enemy without great loss and use it to shoot 2x slow enemy with a 'straight' arrow.
All in all, the game stops to be a challenge when you get 'Town Portal' spell ;)