There are more interesting Linux desktop distributions to choose from than ever before. However, if you're looking for major distros with a great deal of support, you'll want to look at the big four: Fedora, Mint, openSUSE, and Ubuntu.
Each has its own outlook and methods. Thanks to Linux's customizability, you could take any of them and completely revamp it, if you wish. But unless your idea of a good time is operating system hacking, chances are you'll want a distribution that already meets your needs.
Three of the four -- Fedora, Mint, and Ubuntu -- use GNOME as their default desktop interface, although they use it in very different ways. OpenSUSE, on the other hand, uses KDE for its default interface.
Both GNOME and KDE have moved away from their early days when their interfaces resembled that of Windows XP. Each now tries to integrate all available resources and programs, both on the computer and online, into a single, integrated whole.
For the GNOME-based distributions this means, to one extent or another, making the Activities Overview the single portal to access windows, applications and messages. With KDE, this concept is called the Workspace. In all cases, the idea is to give you a customizable environment for running your favorite applications and accessing your information no matter whether it's a local program or a cloud-based application.
There are many ways to try to deliver this integration of the local and Internet resources. Some developers, such as those who worked on Mint, apparently tried to deliver it in a way that's as close as possible to the traditional desktop. Fedora's team, on the other hand, has fully embraced the GNOME approach, while Ubuntu's crew taken a more original approach. Which one will work best for you is really more a matter of personal taste than it is of one being better than the other.
How I tested
I looked at four major Linux distributions: Fedora 16, Mint 12, openSUSE 12.1 and Ubuntu 11.10. I used each for several weeks on multiple PCs.
My primary test box was a Dell Inspiron 530s powered by a 2.2GHz Intel Pentium E2200 dual-core processor with an 800MHz front-side bus. This box has 4GB of RAM, a 500GB SATA drive and an integrated Intel 3100 GMA (Graphics Media Accelerator) chipset.
I also used the Linux distros on a Lenovo ThinkPad R61 laptop with a 2.2GHz Intel Core 2 Duo T7500processor and 2GB of RAM. In addition, I ran them as virtual machines on VirtualBox 4.1.6 on a Dell XPS 8300 with a quad-core Intel 3.4GHz i7 processor, 8GB of RAM, a 500GB SATA drive and an AMD Radeon HD 6700 graphics card.