Which monster do you like the most in Heroes 5 at level 5?

you are comparing them individually, but it would be more accurate to consider their usefulness to the army they belong to.
Here, I think unicorns also stand out, and maybe I'm just being dense, but it seems to me that hydras are also important; they are the only unique units for the Dungeon faction (along with minotaurs), and they are very helpful in battle, even though they are much weaker compared to other units of the same level.