The most useful monster.

if we're talking about the Medusa and the Hide ability, it won't work :) Dragons attack within two squares :)

Added 1 minute ago
I like the Archangel with resurrection the most... it will definitely help a hero if he messes up with a potion

2 Denminator

Is your avatar the Hunter from Kohan, or am I mistaken?

Archangel is good, but it requires huge material costs, and champions are cheaper and can overwhelm with numbers, especially in the early stages of the game, and besides, at level 4, it's preferable to choose angels for Life.

You're mistaken, his avatar is one of the Elven Warlocks from Heroes 5, Sinithar if I'm not mistaken.