Overview of Linux Desktop Environments - which one should you pick?
Unity by Ubuntu
Unity was introduced by Ubuntu in 2010 and since the initial release it has gone under major changes. Unity is, in my opinion, the most exciting DE of the bunch. It combines the best elements of Windows 7 task bar, Mac OS X dock and adds it's own unique elements to provide a quality desktop experience.
The launcher is on the left-side of the desktop and is currently not possible to change the placement. But there are quite a few tools to customize other aspects of the launcher. The launcher has to be the most advanced dock/task bar I have ever used. The dash allows the user to search for applications and files in real time. Also it views recent files, recent apps, and even suggestions from Ubuntu software center.
The top menu-bar consists of indicators and global menu-bar which integrates the application menus to the top panel. Because of the global menu-bar and the left-side placement of the dock, you get more than usual display area for applications.
Unity performs fast and and is very stable compared to the initial release. Unity provides a unique computing experience and I highly recommend it.
Cinnamon Desktop by Linux Mint
Cinnamon Desktop was born to provide users a more traditional computing experience while using the latest software. Cinnamon is now a little more than a year old and yet it is far better than most of the other DEs Linux has to offer. It's core behavior resembles the discontinued Gnome 2 desktop but has number of unique features and excellent customization options. The users can do real time search for applications with the menu and Linux Mint provides number of polished, great looking themes for the task-bar.
Cinnamon is snappy and may be even a bit faster than unity. (Cinnamon is a Gnome-shell fork afterall)
It works great, is reliable and, is one of the two DE's I highly recommend. (other one being Unity)
Gnome-shell is, undoubtedly, the most-interesting and the coolest DE of all. But unfortunately, for most people, it is years ahead of it's time. I personally think Gnome-shell has some great ideas blended in to the DE. It is the fastest DE of all, and is very lightweight.
Once you hover your mouse over Activities button on top left of the screen, a dash opens up with 4 critical features beautifully integrated in to it. They are: file/application search, management of open applications, work space management and quick application launch. Gnome team has done an absolutely wonderful job integrating all of these in to the dash. But like I mentioned, for most people, It is a huge adjustment after using Gnome 2 desktop for years.
It is clear the the Gnome team is working towards building a powerful mobile platform and therefore has removed some of the advanced features that Linux users may depend on. This may turn off some of the advanced users from Gnome shell.
It may take some people a while to get used to, but using Gnome-shell was definitely a satisfying experience for me.
KDE is another popular DE among Linux users. But it's popularity is rapidly declining. This could be for number of reasons. The KDE is desktop is the slowest of them all, (but still reasonably fast), is over-done (visually and functionally) and is over complicated.
The great thing about KDE is that it presents a vast number of features and options to the user. But all of it is presented in a way that it over complicates the computing experience. KDE somewhat resembles windows 7. (I personally think windows 7 interface is cleaner and KDE can be a visual mess at times).
But there are Linux users who swear by KDE. I would recommend Cinnamon desktop over KDE, but you should always pick the DE that best suit your needs.
XFCE is a popular alternative to discontinued Gnome 2. It is light-weight and is more suitable for older hardware. On modern hardware, you are better off using cinnamon or Unity as XFCE offers no speed improvements or unique features over them. Also the project is maintained by very few people and it does not get regular and timely updates. It may not be an impressive DE, but if you are a fan of Gnome 2 and owns old hardware, XFCE can be a good choice.
If you would like to try XFCE, I recommend Xubuntu.
LXDE is extremely lightweight and is ideal for old hardware. It may not be feature-rich or good-looking but it is best lightweight DE linux has to offer. It can be lightning fast on computers that have very poor hardware specs. If you would like to try LXDE, I recommend lubuntu or peppermint OS. In my opinion, peppermint OS (based on lubuntu) provides the best experience.
Of course there are tens of other Desktop environments available. But this article only mentions most popular and widely used environments. If you are new to Linux, I suggest you try all of the above DEs and pick the one you like most.
Also read: Top-5-Linux-Distros-for-beginners