Welcome.
If you are already familiar with Ubuntu, then it is a good choice for you. Of the ones to choose, though, I would recommend staying with a Long Term Support (LTS) version. Those have five years of support so you won't have to do serious changes during that time and can use your machine for actual work. The most recent LTS is Ubuntu 16.04.1 LTS (Xenial Xerus) and it will be good until April of 2021. So if you go with Ubuntu, then 16.04 LTS is probably your best bet.
If systemd is a problem, as it is for some, then
Devuan is derived from Debian but minus the systemd parts. Once it is installed, like with Debian, you will find it nearly identical to Ubuntu.
On Ubuntu, there is a front-end to IPtables. So if you are planning to use IPtables, you'll need to either work with UFW or else disable it and work around it.
If the server edition of Ubuntu does not have "tmux" installed, I would recommend adding it. I find it exceedingly useful.