Desktop layout – While both XFCE and LXDE can be themed within reason, neither desktop screams modern. XFCE tends to provide tools that LXDE lacks, such as a Session and Startup manager whereas LXDE does not. Same thing exactly when it comes to handling multiple monitors.
I will say that for slower PCs, both desktop environments provide a fantastic alternative to running a bloated desktop environment. Besides, with a decent desktop wallpaper, new theme installed and carefully thought out set of icons, both desktops can be made to look pretty good in a pinch. But by default, both are pretty ugly.
Best suited for: Low resource PCs or those who simply want a basic desktop experience. For years, I was a dedicated XFCE user. Not because my desktop wouldn't support a flashier desktop, but because I preferred to stick with something a bit more traditional.
Again, I decided to group these two desktop environments into the same section because they share similar goals. Traditional menus and a commonsense workflow. The difference between MATE and Cinnamon really comes down to bells and whistles in my opinion.
Software – MATE tends to be a bit less flashy than Cinnamon, and its provided software reflects this pretty well. MATE has its own text editor, image viewer, among a couple of other applications. These are lower resource applications that provide a very distro agnostic experience.
Cinnamon, on the other hand, is a product of the Linux Mint project. This means the software and tools found with Cinnamon are designed specifically for Linux Mint users. This means the file manager, system monitor and other integrated software are tied directly into Linux Mint's feature set. Both MATE and Cinnamon utilize a lot of common GTK applications that might also be found with GNOME.
Desktop layout – One specific area where these two desktop environments differ is with their emphasis on bells and whistles. What I mean by this is Cinnamon is a desktop that emphasizes a very modern user experience with lots of extensions and so forth. MATE, by contrast, is closer to XFCE in terms of keeping things simple and functional. Neither is better than the other, they're simply offering very different user experiences. Both are menu-centric desktops, but one offers a flashy user experience while the other one keeps to the basics.
The two core areas where the two desktops share a common layout is with their panels and their use of panel applets. Even though Cinnamon also offers extensions like GNOME, they both share very similar applet options as well.
Best suited for: Both of these desktops are best suited for those folks who love a traditional desktop. Figuring out which of the two is best for you depends on how powerful your PC is and how important a fancy desktop experience is to you. For those people like myself, who genuinely loved using GNOME 2 years ago, MATE is a natural fit. We know the desktop well and have no desire to "upgrade" to a new way of doing things. Others still, need that slick modern feel that Cinnamon provides.
You may have noticed that I left out Unity. The reasons are simple – it's best suited for Ubuntu only and it's not a desktop environment. That's right, it's actually a graphical shell that runs on top of GNOME. So if you enjoy Unity, hey, that's awesome. Enjoy Unity for what it is – a wrapper for GNOME.
What say you? Are you put off that I forgot to include your favorite desktop environment? No problem! Hit the Comments and tell us why you think it's awesome. I look forward to hearing about which desktops make it or break it for each of you.