For a server I would recommend Debian, or Fedora but for different reasons. Debian is a very safe distro. From my experience it can be locked down very well, all though you can do that to most distros.
I use Fedora for a most all of my servers. I feel that it gives you that best two worlds. Security in the it comes with SELinux installed and ready to go out of the box, and ease of use in that you can install most anything from the repos.
Ubuntu is a good beginning linux. It is the distro that I used when I started with linux. If you want a distro that basically works without much work straight out of the box Ubuntu is for you. However I now have my personal quarrels with Ubuntu and the fact that you don't have a root password per-say. But that isn't what this is about.
So there is my two or three cents.