Well, there are several popular flavors of BSD derived UNIX... some being (keep in mind that some of these primary design principles overlap, e.g. OpenBSD is also available on different host architectures, however this is not the primary design objective).
Most of my personal experience comes from OpenBSD, I find it somewhat slow, however the tradeoff in security is usually worth it. I believe their going through some system level optimizations in the near future. OpenSSH is a byproduct of the OpenBSD project, due to the recent ssh1.x remote exploit scare (FreeBSD and anybody that manually linked that RSAREF lib are supposedly vurn, however there is still an ongoing debate), this has gained some momentum.
1. OpenBSD, The Ultra Secure variant.
2. FreeBSD, The IA-32 optimized variant.
3. NetBSD, The Cross-Platform variant.