Actually they are both good slow digesting Proteins. They create a large Cottage cheese type curdle, when they enter the stomach and are attacked by the acids. This makes then be a steady release slow source of High quality protein. Micellar being a very complete unadultered version that has all the various fragile enzymes etc still attached.
You can actually get a very good description by reading the product info. threads for both and various threads and articles on Protein.
Also google is you friend if that doesnt fill you needs.