Ubuntu LTS versions are rather stable as a rule. The last one - 12.04 will be supported for five years - good news! But Gnome3 in Ubuntu (Unity, Gnome Shell - no difference) is too resource hungry. And it needs time to configure it - there's quite a number of various special gui tools that require some learning and it's not that easy to do administrative tasks in a usual unix way in terminal.
But when it's configured it works great and is very stable and reliable.