Linux: I used to run slackware for many years, but in recent years it has just been updated too infrequently. I liked the slackware approach, it was the most unix-like out of the linux distros. And slackware was my first linux, back around 93-94. Rather sadly I believe Pat Volkerding has been suffering from some serious illness over the years, and hence understandably the frequency of new releases of slackware has slowed down.
Nowadays I just grab debian if I want linux. Perhaps/probably there are better things, but I can't be bothered to spend time looking, and debian isn't as crap as ubuntu or fedora. And they still support windowmaker which is my desktop of choice. Yeah, like someone else said, apt upgrade makes me nervous. Whereas pkg upgrade on freebsd works remarkably well; when I upgraded from 13.2 to 14.0 it was perhaps the smoothest OS upgrade I've ever seen, very impressive work.
Something I used to have a soft spot for years ago was frenzy
https://frenzy.org.ua which was a live usb distro of freebsd, from ukraine. It could load itself entirely into RAM using squashfs, like knoppix and DSL. Sadly the developers stopped updating it many years ago. I keep meaning to find the time try out nanobsd or similar things to see if they can work the same way.
I use freebsd quite a lot. Occasionally I try out openbsd and/or netbsd, but so far I've found freebsd better overall.