It really depends what you want to do, for example Novel have the open version http://tr.opensuse.org/MicroSUSE and their supported version OEM. You should look at which distro suits the applications best you want to run and then decide.
I have a large number of portwell boxes. however they are standard X86 machines (even have a VGA port at the back). I run CentOS, ClearOS, Fedora and RouterOS on them no problems yet