Download the first link in your question. It is the official Ubuntu 16.04 image for Raspberry Pi 2 at the ARM/Raspberry Pi - Ubuntu Wiki webpage. The instructions for installing this image are at the same webpage.
Login username is "ubuntu", password is "ubuntu". You will be asked to change the password on first login.
Update: Canonical has released official [Ubuntu Core 16 and Core 18 images for Raspberry Pi 3. The instructions for installing it are at Raspberry Pi | Ubuntu developer portal. As the wiki says: Snappy Ubuntu Core is a new rendition of Ubuntu with transactional updates - a minimal server image with the same libraries as today’s Ubuntu, but applications are provided through a simpler mechanism. A new release of Ubuntu Core is released every 2 years on even numbered years (2016, 2018, etc.).
Ubuntu Core 16 is based on Ubuntu 16.04, and is supported for 5 years.
Ubuntu Core 18 is based on Ubuntu 18.04, and is supported for 10 years.
Ubuntu MATE 16.04 has fully working bluetooth and wifi on the Raspberry Pi 3.
The Raspberry Pi image for Ubuntu 14.04 is no longer maintained. Please use the more recent images instead.