Cloudwatt provides its clients the latest version just release of Canonical Labs of the Ubuntu distribution : 16.04 or Xenial Xerus.
As for Ubuntu 14.04 or 12.04, this 16.04 version is a LTS release – Long Term Service, indicating that this version will be supported and updated during 5 year by Canonical Ltd.
The image includes all system and security updates available as of April 27th, 2016 applied. You will find detailed information about this release on the Canonical Ltd website.
Nota bene : in this new version Ubuntu changed its naming convention of the network interfaces. These ones are no more named ETH but ENS. Be careful if you have automatisation scripts based on these interfaces name.