Which level 1 monster do you like the most in Heroes of Might and Magic V?

Yes, assassins are undoubtedly stronger than Imps, but you forgot that at the beginning of the game and later, there are never more than a hundred assassins, while you can gather about 300 Imps. And first, summon them near the assassin (Hell Gate), and then, while he's dealing with that, run up...
Ranged units have always been weaker than melee units in a one-on-one fight. Their strength lies in the fact that they are convenient for fighting neutral creatures and dumb computer-controlled heroes.