I know this is an old OS, but I'd like to provide answers.
1) I use both FreeBSD and OpenBSD. The reason why I don't use NetBSD or Dragonfly BSD is simply because I don't have a valid use case for them, since FreeBSD and OpenBSD serve me very well already, and I learned about Free and Open before I dug into the UNIX rabbit hole, which led to me into discovering more, like NetBSD, BSD 1.0 to 4.4-Lite, 386BSD, as well as the many non-BSD UNIX systems like OpenIndiana (although I did use OpenSolaris in the past from a live CD), AIX, IRIX, and many others.
2) Yes, both FreeBSD and OpenBSD are my main OS's.
3) I also use CRUX Linux to play video games, because gaming support apart from the handful of FOSS games are lacking on the BSD's, and I use a Debian box for my day job via SSH, because the web backend was made with Ubuntu in mind.
And I also explore other operating systems like OpenIndiana, Void Linux, and even macOS just as a fun experiment.
I might buy 2 more old desktops to play around with NetBSD and Dragonfly BSD more in the near future, and I hope I can one day lay my hands on a Silicon Graphics PC from the 1990's for making Nintendo 64 homebrew using the same tools actual N64 developers used back in the day.
I gave 9front a try, but no matter what machine I boot it on, I can't get the mouse to work.
I also gave Haiku a try, but it always crashes a few minutes after booting.