Knowledge or strength?

I agree with Gunnar, it all depends on the circumstances. Let's consider a walkthrough tournament again. If I need to quickly capture a lot of neutral towns during the game, I will definitely only level up Knowledge to have the opportunity to use the town portal, flight, and dimension door as many times as possible (almost every map has them, you just need to look for them). If, however, it is necessary to break through some powerful garrisons, then I will most likely level up Strength - it is better to have the slow effect last for 15-20 turns, and I will do other things during this time, rather than spend the hero's turn refreshing this slow effect every 3-4 turns!