Which level 7 creature is the best, and why?

The question is, who will he choose as the second, third, and so on?

Yes, I don't know, it's written somewhat unclearly. Here's how it looks in melee combat:
1. Archangel
2. Ancient Behemoth
3. Archdevil
4. Black Dragon
5. Titan
6. Golden Dragon
7. Enhanced Hydra
8. Ghost Dragon