One thing I like about using OpenBSD for my home router is almost all the necessary daemons being developed and included with the OS. DHCPv4 server/client, DHCPv6 client, IPv6 RA server, NTP, and of course SSH are all impeccably documented, use consistent config file formats/command-line arg styles, and are privilege-separated with pledge.
Also it's a really well trodden path. You aren't likely to run into an OpenBSD firewall problem that hasn't been seen before.
Regarding any BSD used for any purpose, BSD has a more consistent logic to how everything works. That said, if you're used to Linux then you're going to be annoyed that everything is very slightly different. I am always glad that multiple BSD projects have survived and still have some real users, I think that's good for computing in general.
The recent addition of dhcp6leased is a great example: Built into the base system, simpler to configure than either dhcp6c or dhcpcd, and presumably also more secure than either.
