I started using FreeBSD in 2002, so it'd have been 4.6 or 4.7. I maintained using FreeBSD on my personal system until switching to macOS in 2009 (Snow Leopard). In between these, I used NetBSD on a couple of older systems and tried DragonFly. Over this time, I used various Linux distributions for my servers.
I switched to using OpenBSD on my personal systems in 2018 and FreeBSD on my servers in 2019. I've been extremely happy with this pairing.
I do most of my programming (in a variety of languages, though mostly C & Forth) under OpenBSD, then do test builds under FreeBSD, NetBSD, and DragonFly. (FreeBSD's support for running Linux binaries is helpful in testing.) FreeBSD's reliability & ZFS make it great for hosting my projects and various private resources.
It might be http://catb.org/~esr/writings/unix-koans/