The desert feel of Marrakesh is unmatched. The two is like walking on a set of Indiana Jones movie. I almost rode a camel there, but did not until I visited Cairo, Egypt a few years later. You’ll see what I mean about Morocco when you finally visit.
It’s been a few years since I’ve been to Casablanca. Its such a magical city full of life. It’s very easy to get lost in the markets. You should go and ensure you have some mint tea on the street corners.