What about OpenBSD, am I a poser or something?! I love OpenBSD. After I get the OSCP certification, OpenBSD is going to be my main workstation again, but not until then.
I will try to detail what my reasons are for going with OpenBSD (instead of GNU/Linux, NetBSD, or FreeBSD of which I'm comfortable using without issue), challenges and frustrations I've encountered, and what my opinions are along the way.
Diving more into stuff from the Pentester Academy, I ended up getting more interested in the Information Security subjects themselves instead of a means to an end to learning assembly programming for the NetBSD kernel. I still want to code NetBSD kernel, certainly, but Red Team stuff sure is interesting.
My goal is to learn enough about assembler, shellcode, and memory exploitation to find and fix bugs in NetBSD relating to those subjects. Maybe other platforms, too, who knows... but baby steps first.