A Knight might not be able to eliminate Vampires right away, especially if they are Paladins and not Knights of Isabel. Teleport is a good spell, but you still need to find it, and where will you get Antimagic then? In my opinion, the most effective spell is not Berserk, but Subdue or Berserk in combination with Griffins + Zealots. If you take Sharp Mind, I think you can inflict significant damage on Haven quite early on. It all depends on the balance of power and the artifacts. Haven is traditionally considered overpowered, but it has weaknesses.

A Knight eliminates Vampires with ranged attacks without penalty and with Adepts – Vampires are the primary target. For Paladins, the targets are Messengers, Warrior Skeletons, or Dragons, depending on which they can reach. Griffins attack ranged units from the air.
Teleport can be obtained either from a Demon or a Warlock if you upgrade their Surprise Attack skill; Grok has it right from the start.

In the final stage, everything depends on the players' skills and the starting lineup. For example, if a Necromancer goes before the Paladins, Subdue is cast, and the Paladins immediately eliminate their stack. Taking Sharp Mind is risky because logistics are not needed in the final stage; it is better to take Defense with Resistance, Agility, and Last Stand.