The advantage of Ubuntu LTS over Debian is that security updates are provided for five years. Since there is a new LTS update every two years, you have a three year upgrade window, as opposed to the year-long window of Debian.
But the documentation is completely lacking. Debian outlines exactly what can go wrong with upgrades between major versions, what assumptions are made, and so forth. Ubuntu has basically no documentation at all.
Ubuntu is basically Debian with a bunch of extra stuff you neither want or need on a server. Such as X11.
