CentOS 5 would be my personal choice as well.
Although I believe both share their heritage with RHEL, I think xavierp nails it when he says Fedora is a bleeding edge distribution. I think it may in fact be more or less considered a testing or proving ground for some potential features or applications not yet completely ready for a production environment. CentOS on the other hand, if I am not mistaken, is RHEL recompiled from source and simply redistributed minus all the RedHat branding. I have used both on my personal server projects, and CentOS has been hands down my favorite, as well as rock solid.