Leonardo’s angel stands out for the eloquent pose, the folds of the garments, the sweetness of her expression, all missing in the other angel. Look at the Madonna of the Rocks, you will see the similarity with this angel, but more expressive and beautiful.
Dan, it was normal to have other artists take over part of a painting. In the Verrocchio studio, there were apprentices who went on to be famous, like Leonardo.
Yes, spankalib, #15 would be considered Northern Mannerism or pre-Baroque.
Wow eta - thank you! Great explanation. Thanks for taking the time to edumacate me!