I would recommend Linux Mint over Ubuntu 99.9999% of the time. The theme is better, the mintMenu is awesome, it comes with better software, and you aren't constantly getting kernel updates (and having to restart).
In other words, I consider Linux Mint a patched version of Ubuntu.
Do you have any suggestions for the best OS if I was to run a server?
I've got numerous spare computers.
I've had great experiences with Arch Linux on my server. You get to build the whole system from the ground up. It's awesome. I've used both it and Ubuntu Server Edition, and I would recommend Arch. USE, Debian, Arch, or anything would be fine, though.