Magic in Heroes of Might and Magic V.

Dark magic, and especially the higher-level dark spells, is the most promising choice because Berserk, Blindness, and Enslave always work, and their effectiveness is proportional to the strength of the enemy army. Unlike Chaos, for example. I think Enslave is overpowered. It can be removed, but not every hero has high-level Light magic to dispel the spell with a 100% chance or cast Antimagic up to level 5. And a Knight, in a game against Necropolis, for example, can take Weakness to Darkness and Darkness Seal :) I'm not even talking about the fact that a weak Dark Mage can use Enslave to brutally slow down the remaining stack and then finish it off with the entire horde. Such games are rare, but usually, the one with mana left wins, because by the end of the battle, Chaos also becomes more dangerous, and its spells start to deal significant damage. Not to mention Grief, Celestial Shield, Phoenixes, and Elementals :)

Berserk is better because the creature immediately moves and attacks with doubled fury (or something like that in the description).

Bonus damage is determined by magic skill and spell power. But the main thing here is not to miscalculate and cast the spell on those whose turn is very close to your hero on the initiative scale. Then you can be sure that your troops will not suffer, and you can predict the possible targets of the spell. The hero is powerless against Berserk if he doesn't have Antimagic.