Web server development platform, Red Hat or Ubuntu
davidw: Redhat is a commercial product that you have to pay money to use.  CentOS is supposed to be a pretty good server OS.However, I'd choose Ubuntu (and have) for this reason, amongst others: you can run the same OS on your server as on your desktop.  You might be able to do that with Fedora, too, but Fedora is not Redhat's main focus, like Ubuntu is with, well, Ubuntu.