Which level 5 monster is the best?

In terms of speed and morale compared to early-game units, the Minotaur is the best choice without a doubt. However, in the late game with a large number of units (starting from 35...), Gorgons become the best option. Gorgons are most effective at levels 6 and 7 – this is their optimal level. Also, it's convenient to take 6 groups of one Gnome and 30 Gorgons and bombard Utopia without any losses.