Which level 5 monster is the best?

Tested 1v1 matches. The Gorgon only kills the Troll if she gets a lucky critical hit with her breath attack; otherwise, she loses. The Minotaur easily defeats the Troll. The Evil Spawn wins about 1 out of 5 battles. The rest lose due to regeneration. Also, the Vampire Lord deals about as much damage as the Troll does – after 36 turns, the Vampire had 31 HP out of 40, and I ended the battle because I was getting bored.