Of all the great OSes, NetBSD seems to get the least fanfare but it's always been my favorite. It's fast, secure, and due to a well reasoned architecture it works on everything. pkgsrc is amazing. They also have a very helpful, friendly community. It especially warms my heart to run `ps -ax` on a new install and see all of about 10 processes. The OS feels lean, neat, and organized, and I feel like I know exactly what is going on, where to find a given file, etc.

These special strengths -- vast hardware compatibility, rump kernels, now full reproducible builds, are all enabled by a greater underlying (and seemingly underrated) technical excellence.