Mostly not having to worry about removing shopping lenses and any other things. It's a growing lack of trust in Canonical.
I don't use my Linux boxes as a desktop most of the time otherwise I would be giving XFCE a proper try. In fact the main desktop use is child use so I don't want to change it too much.
Not challenging, just interested. Both have fallback, both allow the installation of XFCE4 desktop, both have the Lubuntu-desktop packages?