Ubuntu is one of the most user friendly Debian based Linux distributions. It curently has a LTS version out, Ubuntu 14.04, codename Trusty Tahr. As of the older LTS 12.04(Precise Pangolin) both the server and desktop version will have support for 5 years. Meaning they will have security updates for 5 years. After 5 years it is wise to switch to the newer LTS release.
Welcome to NewOS! For those that don't know it yet: NewOS is a site dedicated to helping you choose your new Operatings System. All operating systems here are Linux based. What is Linux? Linux is a kernel, which is the piece of software that lies between the hardware and the applications(Firefox, LibreOffice). Now, Linux is free, but still has a licensing on it(GPL v2)