The Reg guide to Linux, part 1: Picking a distro
Who's top of the table and who's going home
The best of the rest
There are dozens of smaller players out there vying for your attention, but most aren't really worth the time unless you're already an expert or have a specific function in mind.
For instance, if you just need something to get a really old, low-spec PC running for the spare room or ready to give away, Damn Small Linux and Puppy Linux are both good candidates. Both work well on a Pentium II or Pentium III-level machine and might even run on a high-end 486 at a push.
Knoppix is a live CD – in other words, a complete Linux OS designed to boot and run from CD without being installed. Ubuntu and several other distros ship as live CDs these days, but the environments are limited and only really intended to check that everything works on your PC and then to get it installed. Knoppix is intended to be used this way and is a great tool for recovering data off crashed or virus-infested PCs, diagnosing problems, checking internet connections and so on.
MEPIS is a custom respin of Debian with good multimedia support. It's got some devoted fans but there isn't much to set it apart from the far more mainstream Ubuntu or Mint.
Gentoo is the software equivalent of a liquid-cooled overclocker's PC: to install it, every component is recompiled for your PC with your preferred optimisations. In other words, it takes ages, you need to know exactly what you're doing and at the end it's only a few per cent faster but looks unlike anything else. It's not really worth the bother. Sabayon is a more polished liveCD version if you really want a look.
Similarly, Arch Linux is a tweaker's dream, aimed at expert Linux users, as is Slackware, the oldest surviving distro, with very conservative – ie old-fashioned – installation, packaging and admin tools.
The highest-rated non-Linux open source OS is FreeBSD, parts of which form the underpinnings of Mac OS X. Don't expect Apple-like sophistication, though – FreeBSD is adamantly old-school, aimed at skilled Unix users. If you want to play with an easy-to-install version, try PC-BSD, which has nearly Linux-like levels of polish.
To be honest, unless you have some other reason, such as wanting to get into working with enterprise distributions such as RHEL or Novell's SUSE, for a first-timer or if you're giving Linux the first go in years there's no good reason to look beyond Ubuntu. Don't bother with any of the special “editions” or remixes – Ubuntu itself is the most professional offering around and it's possible to go from a blank machine to a working system with all applications and everything in well under an hour - considerably faster than it would be with Windows.
Tomorrow, we'll look at preparing your machine to dual-boot between Windows and Linux. ®