My history and choice of OpenBSD is more personal than technical.

I started to code actual programs for Unix (until then I have only written school stuff and exercises) in 2020. I'd took advantage of my free time (pandemics) to learn new stuff. I first used GNU/Linux manpages to understand the library and system functions, but quickly noticed that some of them are too verbose, others are too shallow, and all of them lack cohesion and do not fit together. Then someone told me about OpenBSD manuals, so I started to use them as learning material.

Right after that I discovered that the code of OpenBSD core utilities was very readable. So I used them to learn and re-implemented those utilities (like indent(1), expand(1), vis(1), etc) just for learning (and for fun). By studying their code, I spotted a bug in one of those utilities, and it was, iirc, my first bug report and contribution to an open source project. (And I think that at that time I was not even using OpenBSD, I was just studying their code on Linux).

Then I gave OpenBSD a chance. I continued studying the code, and spotted a few more small bugs. One may think that discovering bugs (even being small bugs) in an OS is a red flag to avoid it. But in my case, it made me more interested in the system and to explore it. And for the first time I feel myself part of the development of a FOSS project.