What is more important: luck or fighting spirit?

Yes, in general, good morale and luck are key, but as skills, they only work along the path that leads to failure. I remember a battle in the Fortress against a Castle, where both had +3 magic resistance. That was intense. The elves shoot once successfully, then morale kicks in, then the Crusaders hit, dealing 2 damage, then luck kicks in, then morale again, and then they get a lucky hit back, and so on... The shouts of "Oops!" "HA-HA-HAA" "O-o-o-o-o" and "E-E-E-E" echoed throughout the house. P.S. The Fortress won.