What is more important: luck or fighting spirit?

well, everyone except Necropolis and Elementalist factions gets morale), and for this pair, Good Luck;). Morale is better; that second turn isn't always for an attack, but for various actions, of which there are many, besides the two mentioned above. I usually increase morale (though sometimes I don't take it for a castle – what's the point when you already have a +3 bonus?).

Added 2 minutes later

Without a doubt, morale is better. Remember how annoying it is when you defeat a small army, hoping for angels, and suddenly the morale of the griffins ruins all your plans, and you think about how to even get out of this mess!

Exactly! It's so annoying in the Dungeon when the griffins' morale is good =), and for you, it's always bad luck; it never works. I've seen a -2 luck in the first and second Heroes games, but has anyone ever seen Misfortune in practice?