My favourite linux distro is Debian. Ubuntu Server is also great, but in my case generally I only need a LAMP server (Linux + Apache + MySQL + PHP), without big network responsabilities (mainly on intranets implementations). And, finally, Ubuntu is Debain based. Because this, I choose the lighter option, Debian. For graphic interface, I prefer LXDE, one of the lightest actually.
If it was only install and bring it up, would be great. Otherwise, when a server is exposed on Web, it becames to be target of many malicious bots, which searches security fails over all internet , IP by IP, almost port by port.