Novell openSUSE 11.1
If I could use one word to describe openSUSE 11.1, it would be "solid." There may be a way to knock this version of openSUSE off-stride, but I haven't found it yet. In the past, updating openSUSE could be a pain, thanks to what seemed like endless development problems with its update routines. Those finally appear to be history.
Where I see openSUSE operating best, based on my look at the release candidate, is in the office. Whether you use it as a desktop system or as a server, openSUSE is the most business-ready of the community distros.
It starts with Novell's customized version of OpenOffice 3.0. With this version, you can read and write to all Microsoft Office files, including Office 2007's Open XML formats.
On the server, however, is where openSUSE really shines. The installation routine lets you automatically set up Web servers, file servers, Internet services servers, database servers -- you get the idea. Any Linux distribution makes a great foundation for servers, but only openSUSE makes it so easy to set them up.
OpenSUSE, like the other Linuxes, also comes with virtualization apps KVM (Kernel-based Virtual Machine) and Xen. In addition, openSUSE includes my favorite virtualization software: Sun's VirtualBox. In my experience, VirtualBox is the easiest virtualization program to set up and works extremely well on openSUSE.
Finally, while some people dislike Mono, the open-source Linux version of.Net, because of its Microsoft connections, openSUSE has the best integration of Mono and Linux. This functionality, combined with Novell's other Windows-network friendly features, makes openSUSE not just the best of these distros for business use, but for integration with a business' existing Windows infrastructure.
Since I'm frequently working in hybrid Linux/Unix/Windows business network environments, openSUSE is my own Linux of choice. If that's you too, then you should look into openSUSE as well.