What is your favorite ultimate ability for that class?

Warlocks have the "Fury of the Elements" skill, which also provides a good boost to damage for both the army and spells, albeit in some cases.

For Wizards, it's a great skill! :)

Only for Warlocks, besides the "Spell Affinity" skill, it's desirable to get the "Mana Absorption" skill as quickly as possible. In the campaign in version 3.0, I decided to do without it. As a result, in the 2nd mission, after reaching the development limit for my Railegh, he had 50 mana in reserve. And in the 3rd mission in version 1.5, in some battles, Railegh spent 150-200 mana. I started the campaign again from the first mission, focusing on getting the "Mana Absorption" skill.

I agree that it's a great skill for Wizards. However, a Wizard with only 1st and 2nd level spells will have a hard time if, within the first 1-2 levels before getting "Spell Affinity," he is attacked by a well-developed hero of the same level under human control.