Sometimes spirits, at least the ones who do interact with us, take forms that they know we'll be comfortable with.
Others just don't bother, and the results of that approach can certainly be interesting!
Besides, when most people think of angels, they don't think of a four-headed beast with wheels?but that's what's actually written out in the Bible. In paintings, the feathered wings could be an influence of Greek paganism: the muses, the wind deities, and Nike (goddess of victory, not the sports shoes), were all traditionally portrayed as human-shaped with feathered birds' wings and that influenced the image of angels.
They could be neither. They could be eyeless towers. That would be interesting. Just because it isn't a recorded form of a categorized "choir" doesn't mean that it's impossible, but I'd be wary of sharing that information with people who are precious about traditional names and images following an already-established canon instead of discovered through personal experiences like that.