I'm about 1/2 tempted to answer 42! But here are my thoughts:Fedora Core
is a great mainstream distro. On the ARM platform however, they provide a root file system, and leave you on your own to build a kernel to hitch it up to. If you aren't already strong on Linux, don't bother. There aren't a lot of packages available for it yet either. Oh, and if you want graphics (more important to the OpenRD than SheevaPlug) then you'll have to add those packages after the fact.http://fedoraproject.org/wiki/Architectures/ARMUbuntu
is a great distro (built on Debian) but as of version 9.4 they quit supporting the ArmV5 processor in the Kirkwood platform (Sheevaplug, GuruPlug, OpenRD). If you use Gumstix they run ArmV7 so you're still in.http://www.ubuntu.com/products/whatisubuntu/armAngstrom
Linux is pretty slick. They have an on-line builder, so you can choose the packages you want. They have good kernel support as well. There are fewer packages than some of the other distros, but they're still good.http://www.angstrom-distribution.org/Debian Lenny
- Deiban Lenny is the longer term supported version of Debian Linux. It's solid, but Squeeze
has more packages, and I've not had any problems with it crashing on me. On the OpenRD-Client (the big brother of Sheeva/Guru Plug) I run a custom kernel put together by Frans Meulenbroeks http://james.99k.org/openrd.html
which includes all the drivers for video and sound on the OpenRD (it's not mainstream yet). He's done a much better job with it than I've been able to do on my own, and I've had really good luck with it. At any rate, Squeeze seems as solid as Lenny to me, so I'm sticking with it.
SuSE: You're out of luck, they don't support ARM.
Gentoo: You have to compile it yourself anyway so it's not exactly plug and play http://www.gentoo.org/doc/en/handbook/handbook-arm.xml
That's my two cents...