Upgrade or alternative upgrade?

I don't know, I like to use Archangels; I don't think they are weaker than Seraphs. Seraphs just have tougher spells (Divine Retribution), but against humans, cavalry usually takes the first hit (at least, when playing against humans, this is a normal tactic), which means Divine Retribution shouldn't be used too quickly. And later, Seraphs might even die.

Archangels can even successfully resurrect someone early on. In my case, it's usually Axel's cavalry.