At least most desktop managers (gdm, kdm, etc) allow you to establish a preferred desktop environment. You can have KDE, Gnome, XFCE, Unity, LXDE, etc... all in

At least most desktop managers (gdm, kdm, etc) allow you to establish a preferred desktop environment. You can have KDE, Gnome, XFCE, Unity, LXDE, etc... all installed, and pick which one you want to start your session with. The only thing that becomes messy is that some applications might use Qt, others GTK, and the themes might be inconsistent. Fortunately there's a GTK engine for Qt and a Qt engine for GTK that allow you to have a more unified experience. The menu also might end up with many applications and the preferred applications for each file type can be a bit hard to manage when you have multiple desktop environments installed.