Initial goal was to setup an SSH jump host with Debian. Then the realization that I don't actually need all the extra bells-and-whistles, just something that is designed to be secure out-of-the-box: OpenBSD.
Some features of OpenBSD that makes it attractive:
Documentation has been praised to be complete and well-written.
Userland software are more tightly integrated and coherent.
Exploit mitigations are enabled by default.
And then the disadvantages:
Likely outdated design (e.g. this
article focuses on missing MAC implementation on OpenBSD, some assertions on, say, LPE are not limited to OpenBSD, but overall still valid).
Less hardware compatibility as well as online help, i.e. less modern.
Anything beyond the core suite of services provided by the base system will inevitably introduce vulns.
Misc
This YC comment captures the feeling well:
What are some pros and cons of using OpenBSD instead of Linux?
Pros: htop only fills half of your terminal, and you know exactly what each process does because you put them there. A few well-written man pages are the complete documentation of the system. The whole thing is run by a handful of shell scripts.
Cons: exactly the same text, but read with a different tone.
From my first usage, it really is half a page tall. Though to be fair, Debian itself is also fairly minimal (until I added a couple of network services).
Other comments on FreeBSD, including the good and the bad (mostly security-related). FreeBSD is probably more commonly used as a daily driver, and thus has more traction, e.g. FreeBSD new user guide.