Which level 2 creature is the best?

The best unit is the archer. The main thing is not to lose it in the early stages of the game, upgrade it, and enemy units will fall at your feet, which significantly saves mana. Consequently, you gain more experience. The best ranged units of level 1-2 are those that shoot or attack without retaliation (respect to harpies). On a 200% difficulty, you can fight with them without losses, and in the main battle against the enemy, 150-230 archers can destroy or severely damage level 1-2 units (or at least inflict significant damage) before they even reach you (I mean a real battle where there is a defense in front of the archers, not a 1-on-1 fight). Besides, in the 3rd-4th month, level 1-2 units become a burden; archers don't leave the battlefield until the very end.