Which level 7 creature is the best, and why?

This is nonsense! Under these conditions, in 4 out of 5 cases, Behemoths will defeat Archons due to their -80% attack! But Phoenixes are definitely the best, simply overwhelming everyone with their numbers and speed! And then, of course, Archons!

I already said, if you're not lazy, test it in the editor! Even 1000 vs. 1000, Archons will defeat Behemoths! Have you seen their stats? Their defense is almost twice as low as Archons, and their attack is also lower. And those 80% would only work if the heroes have the same defense parameters (at least 13).