Ubuntu 14
14.04.5 LTS will end April 2019, so for those who can live with some outdated software, it will probably do for a while.
Ubuntu 15
15 is not with us anylonger so I let it rest in peace.
Ubuntu 16
16.10 is dead but 16.04 will be alive until April 2021.
Ubuntu 17
17.04 is recently deceased and 17.10, the contemporary one, will be with us until July 2018 or when 18.04 has grown up.
Ubuntu 18
18.04 is still in testing mode, with planned release April 2018
My comments
18.04 will be released coming days, as I write this, and I suppose it hasnt matured yet and 17.10 are fading out.
Of the remaining ones, 14.04 has some obsolete software that not always has to be a disadvantage as it has the packages old software like 11G-XE needs. I dont know of any problems, but I suspect some lost packages like “pdksh” could give problems running some scripts, but i’m not sure. I didnt find any scripts with any pdksh z.bangs, but dont know if any other product uses such scripts.
So my personal choice is ubuntu 16.04 as it is quite recent and stable.