For me it’s either Vecna or Predathos.

I mean... Obann, Lucien, and Thordak aren't even in the running. Ludinus wants to free a god, Vecna became a god, and Predathos eats gods for breakfast.

I think it's a tough competition between Vecna, Ludinus and Predathos. A god, a 1000 years old mage that wants to release a god-eater, and the god-eater himself.

I know it's crazy to say, but I prefer fighting Obann or Lucien by far. Even Thordak honestly.