OpenBSD is also my go to. The only caveat I'll throw out is when I upgraded to gigabit internet I discovered OpenBSD on the protectli FW4B couldn't keep up. In fact in iperf benchmarks it pushed ~300 Mb/s to FreeBSD's 600 Mb/s. Considering all the work done on Linux's network stack I plan to try it next to see if I can squeeze any more out of the hardware.

Just means anyone who wants to try OpenBSD should spec something a little more powerful than that appliance.