What is your favorite ultimate ability for that class?

In my opinion, the Haven ability would look much better on the Orcs; just imagine: "Great Reinforcement" (300% damage). :)

It would also be good to give the Haven faction a special ability called "Great Counterattack" (+50% damage on counterattack, stacks with the Knight's offensive bonus). And make upgrading this special ability more challenging.

P.S. I voted for Call of Urgash. With skillful play, Nimue with this special ability can easily defeat Elves and Dwarves (even if they have their own special abilities).