Which level 7 creature is the best, and why?

I think this way: black can definitely defeat an archangel, but: in the gameplay, the archangel restores +1 to morale and has a high priority,
only the phoenix has a higher priority, meaning the archangel uses magic first. The most important thing: don't forget about a spell that affects everyone who doesn't have immunity;
it works very well: clone

Listen, Zhenya, you express yourself so amusingly... I mean this: you say that black can quite possibly defeat an archangel - that's interesting, how? Have you checked it yourself, for example, draw a map in the editor and see what? how? and at what cost?
Furthermore, you write that archangels will go first, morale, etc. - it's silly to argue with that, but isn't complete immunity to magic weaker? - I don't think so.

conclusion: in a game situation, it's better to have an archangel
otherwise, it will turn out the other way around :)

Again, I disagree - game situations can be different ;)