OpenBSD vs FreeBSD (Score 1)

OpenBSD has a focus on security and I believe they were the group that developed pf. Out of the box, OpenBSD will be pretty much configured well for a router. Also pf on OpenBSD uses a newer syntax. The install process is pretty basic and some of the terminology used for partitioning disks may be confusing for someone used to Linux terminology. In-version OS updates are handled by downloading patches and recompiling from patched sources. Major OS updates come out every 6 months.

FreeBSD has a focus on being a friendlier OS to work with. The kernel exposes many more tunable options and performance is generally considered better on FreeBSD. pf uses an older syntax that was forked off at some point and may never update to the newer versions OpenBSD offer. FreeBSD has a lot of other features like ZFS, which can be a big deal for Samba. The installer is more friendly and OS updates are handled through a fetch/install command. Major OS updates come out frequently according to a set schedule.

I have the expectation that FreeBSD will support new hardware faster than OpenBSD. I think most people serious about OpenBSD will be running it on a machine with Intel network cards. Other nics (realtek, broadcom) may work but sometimes have problems under heavy load on OpenBSD.

I use OpenBSD for my routing/firewall and a separate FreeBSD system for samba/fileserving. I don't expect any problem with running samba on OpenBSD alongside the firewall, but you won't have the benefits of ZFS, which is a big deal for me.

pfsense and m0n0wall are both based on FreeBSD, due to performance.

Unfortunately I don't have as much knowledge about NetBSD.