I've used almost every desktop on the planet, but Ubuntu 15.04 with the Unity 7 interface may be the easiest. Heck if my now 82-year-old mother-in-law can be an Ubuntu user, you can be one too!
For four years now, Unity has made Ubuntu as simple as clicking on the app, and you're off and running.
The applications, like the default Firefox browser, spring up immediately. When you minimize them, they fold back into the Unity panel on the left.
At full-size, applications, like the latest LibreOffice office suite, are as easy to use on Ubuntu as they are on any operating system.
Want a new program? There's no need to master shell language commands or the intricacies of apt-get, you should simply browse through the Ubuntu Software Center, its app store, or search for your application by name.
Controlling how Ubuntu works is also mindlessly simple. All the controls you're ever likely to need are easy to get at and easy to understand.
Want to work with your network? It's no fuss or muss with Ubuntu even if your network, as mine is, is a complicated set of Linux Samba servers, Windows 2008 and 2012 servers, and Apple Time Capsules.
If you've been frightened off of Linux because you think it's too hard, take another look. These days its easy-peasy.