Ubuntu is a great introductory distro for a beginner, but it is robust enough for the long term user. Canonical is the company behind Ubuntu and they have a development team for testing and compatibility. They also use a LTS (Long Term Support) model that means once the LTS version is released, it will be security supported for five years. This is a great release model for the person that wants to create a system and not worry about changing things around for a while. Of course you can always update to the latest full release if you would like.
Ubuntu is generally unique because of the Unity Desktop Environment created for the official Ubuntu release, but you can find this distro available with almost every desktop environment if you want to use the system but do not care for Unity. I personally have grown to like Unity, but it is still not as fast for me to navigate my work as it is in the Cinnamon Desktop Environment.