Hi Jooccer
That depends on what else are you planning to do with the server.
If the HW will be used only as XBMC, maybe the best would be to install XBMCbuntu (
http://wiki.xbmc.org/index.php?title=XBMCbuntu ).
If you also want to use it for other applications, Linux Mint is a great OS and both Mate and Cinnamon are OK (Cinnamon used to be "too new" but with next Mint release it will get a great boost, while Mate is very stable and "classical" but lately nothing interesting is being added). But as Teeedubb said, it won't be a great idea to run XBMC inside Mate/Cinammon desktop, the best is to configure it as an independent session fro the login screen (this means, you log-in directly into XBMC, without loading the desktop)
In order to do so you can check this link:
http://youresuchageek.blogspot.fr/2012/0...linux.html the section that starts with " If you installed Ubuntu Minimal, set the Xsession to automatically start with XBMC: " Please note that the link has other interesting linux tips, but you should ignore everything related to XVBA, Catalyst and display drivers of that link (those are special instructions for AMD)
I've installed my system that way. When you power it on it automatically displays XBMC in the main screen (my TV), but I can also run a remote mate-session via nomachine from an old notebook that I use as a dumb terminal.
Hope this helps