Maybe I should re-think my decision.
What I want most is long-term stability, trying to guess which platform will be most stable and well-developed a decade from now.
Canonical looked like it was spiraling down a consumer-oriented rabbit hole, chasing phones and such.
I could live with Unity, I was getting used to it after a rocky start.
People really seem to like Mint.
I also lost faith with Ubuntu - silly arguments over window control positions, proprietary utilities, very short support time, an apparent growing lack of community support.
I was using CentOS as my development OS in a virtual machine, nothing wrong with it at all. Well supported, long support (much longer than Ubuntu). The only downside is that packages are necessarily old and not updated frequently, which is fine if you just want a stable well-supported system, but unfortunately I had an increasing need to install more and more newer packages that just weren't supported without installing an increasing number of newer libraries.
I tried Arch - far too much reading, I needed this VM up and running fairly quickly. Also you shouldn't just update Arch willy-nilly without reading all their latest updates and warnings. Again, too much reading.
openSUSE - as described above. I used SuSE back in the day, and work even bought a box set with thick paper manuals included (can you believe that!).
So I tried the newly release Debian which, apart from the kerfuffle around systemd, seems to be doing the job. It is not supported for as long as I might like (not as long as CentOS), but so far so good.