OpenBSD is compact and secure posix compatible and traditional unix. Unmatched man pages (seriously, everything else is trash compared to OpenBSD man pages). Developers know their game and follow strictly vision set by Theo de Raadt. Less features, more stability. Slower development pace, but it is easy to follow. It’s peaceful system without stupid linuxisms or gnuisms. Try it! I run it on my desktop and on servers. Negative points: its marginal, not always well supported, not as performant as other bsds or linux and filesystem is lacking journaling and other modern features (this can be painful sometimes).
FreeBSD is great option too! Especially for fileservers (zfs!). If you have nvidia gpu go with FreeBSD as it is not supported at all in OpenBSD. I am using intel gpus and they are problem free with OpenBSD (AMD should be ok too). OpenBSD is mostly politics free.. it’s like: shut up and hack :)
In Linux world I really like Alpine. If I want more customizations, Gentoo is best for fine tuning everything (like running all clang based system with musl and openrc init). Devuan is non woke Debian with init freedom (no systemd :)
OpenMandriva is ok, I tried it shortly after Lunduke mentioned it, but not my cup of tea.