Which skills are best for a hero?

It's not something you can answer right away. The parameter you mentioned (the hero's morale) isn't the only factor that determines whether the unit you specified will join your army or not. I don't think it makes sense to move the diplomacy information from the manual to this forum thread. I understand that not everything written in the manual is immediately clear, but you need to try to understand it. However, I'm also curious about which undead units can join our army, even if it's for a price. We need to try to calculate and create a kind of table for unit recruitment, for example, based on the weekly increase of undead creatures in our city and the number of neutral creatures on the map, depending on their quantity: few, several, group, squad, many (I think a larger number won't join us).