A few years ago you'd have to decide between KDE and Gnome, with the 3rd way choice of Xfce for slow computers. With the controversial release of Gnome 3, the Gnome "faction" split into 4: Gnome 3, MATE (a continuation of Gnome 2), Cinnamon (developed by Linux Mint), and Unity (developed by Ubuntu). There was also the release of LXDE (soon to be LXqt), a new low-resource desktop environment aimed at old computers and therefore in competition with Xfce.
I have also added Enlightenment, Pantheon, and CDE to the comparison, as they are also (kind of) relevant desktops for Linux/Unix systems. In addition to that, the desktops of Windows and Mac OS X are included.
If you spot an error, please leave a comment.
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