CentOS 5
I’ve been using the CentOS Linux distribution for almost two years now. CentOS is based on Red Hat Enterprise. The reason I started using it in fact was that we were using RHEL on a project at work and I wanted to start using it at home so that I could become more adept with the OS, but of course I was not willing to pay for the commercial version on my own dime. To be fair though, I recommend RHEL to clients.
CentOS 4 has worked very nicely for me and now I have a chance to set up a new machine and I see that CentOS 5 is out.