Do you prefer armor or attack?

Here's what I found in the documentation regarding damage calculation: The amount of damage is modified based on the difference between the attacker's Attack stat and the defender's Defense stat. If the attacker's Attack stat is higher, the damage dealt increases by 5% for each point of difference, but not more than 400%. If the defender's Defense stat is higher, the damage dealt decreases by 2.5% of the nominal damage for each unit of difference, but not more than 70%. Then, the damage may be further reduced if the defending unit has the Shield or Air Shield spell applied (this spell does not work when reflecting attacks from city towers – instead of reducing damage, it doubles it. Most likely, this is a programming error) or if the hero leading the unit has the "Weaponsmith" skill.