Steven J. Vaughan-Nichols provides a nice guide toward Linux choices. It's short, so I copied most of it over.
(Links at source.)
With so many desktop Linux distributions, unless you're an expert it's hard to know what's what. Since I've been using desktop Linux almost since day one, and I've used every major distribution out there and many of the minor ones, I think I qualify as a desktop Linux expert. So here's my quick and dirty guide to picking out the right desktop Linux.
You're sick of Windows, but you don't want to spend a lot of time learning Linux. If that's you, get a pre-installed Ubuntu Linux PC. Ubuntu is easy to use, and you can get ready-to-go laptops from Dell and System 76 among other companies.
You no longer want Windows, or you're not interested in 'upgrading' to Windows 7, on your business PCs, but your office is using a Windows-based server infrastructure. If that's you, you're in luck. While some people really dislike Novell for partnering with Microsoft, if you want a Linux desktop that will work hand-in-glove with Microsoft servers and AD (Active Directory), Novell's SLED (SUSE Linux Enterprise Desktop) 11, is for you.
You want nothing to do with proprietary software what-so-ever. There are several desktop Linuxes that steer clear of any contamination from closed-source programs or drivers, and the Free Software Foundation has an up-to-date list of closed-source free Linux distributions. Of these, I like gNewSense the best.
On the other hand, if you want a Linux with some proprietary goodies, such as support for some Wi-Fi hardware or Windows media formats, you have two good choices. OpenSUSE, which like SLED, works well with the business side of Windows, and Mint, which is built on top of Ubuntu. I use both a lot and I can heartily recommend either.
If you want a Linux that has great community support, but is also right on the cutting edge of technology, Fedora is your distribution of choice. Fedora 11, I might add, is also an excellent distribution in its own right.
Finally, if you just want a Linux that works really well, let me recommend one of my personal favorite Linux distributions: SimplyMEPIS. MEPIS, which is based on Debian is remarkably stable, easy-to-use and full-featured Linux.