I'm gonna say this. "Technically", those Angelo forms are indeed demons, which makes the demons win by default. But that's just a fancy way of me saying that neither is cooler. They're all cool in their own right.
But, do the Alto Angelos count as a transformation? Their description says that they used to be normal order soldiers. I think the Alto Angelos are the coolest. When I first saw Sanctus posing as an Alto Angelo, I was like. "Wow." And then I saw them as normal enemies and I thought he had cloned himself. Am I dumb or what? >_<