Played around a bit with Debian GNOME. I have to say it's better than I thought, especially for beginners, because it is very streamlined and easy to configure. Less fiddly & more pretty than MATE, and not the non-free disaster that is Ubuntu 😬
Might default to Debian GNOME from now on, when the client has no idea. Debian MATE only for people who already have a bit of experience with GNU/Linux. We'll see 🙂