IMHO you either want a server, or you want to play. For desktops/playing out of your shortlist I'd be looking at Fedora 8. Nice desktop, well specced, has lighttpd/apache2/sql etc all in the repos and you can get your hands as dirty as you like while you learn. You also have gui tools to fall back on for if (when) you get stuck.
Forget wanting to escape package management, it's there for a reason. Who wants their server going down because the latest release of apache didn't compile right from source and you can't chase down the problem because you're only learning?

Use a package manager, and do your learning on the real stuff (server side admin, config etc) before you start messing around outside of package managers imho.
Ubuntu has a server distro - "Ubuntu Server" lol It's lean, fast and has no GUI - just a command line. You'll learn quick enough doing stuff that way and at least have the stability and reliability of apt to fall back on while you learn. Install takes about 10 mins for the base system, then you can ssh in and start setting it up
Debian is another great distro for the server, and can be as lean and fast as you want it to - with or without a GUI/DM. Debian also release security patches daily, which is useful when an exploit comes out.
CentOS is great, but is also rpm based and slower than Debian/Ubuntu. Don't get me wrong, although I run Debian at home my main box is Fedora (i.e. rpm based) so I'm not starting a flame war - just pointing out the obvious

As was said above, while CentOS is basically rebranded RHEL and therefore a great distro and also handy for learning the system (for work), their forum members can be really snobby/elitist and if you aren't already a sysadmin, all round Linux guru and can't post in binary they seem to ignore and/or flame you LOL It's a real shame, because it has the potential to be a great distro and community.
Hopefully you've got some new info to think about, personally I'd go with Fedora for a powerful, configurable desktop/server distro with good support. However if it's server only, I'd stick to Debian or Ubuntu server personally. JMHO
