Which level 7 creature is the best, and why?

I think Ley wanted to draw attention to the quantity (200 HP * 4), as well as the speed (21 - unconditional turn priority...).

Absolutely, Zhen! An increase is a good thing :), and I won't even mention the turn priority, but in my opinion, their main advantage, besides everything else, is fire immunity - in most game situations, they can compete with many level 7 units... ;)