I have switched to FreeBSD after spending a few months banging my head against OpenBSD. OpenBSD is a nice O.S., and I really didn't want to switch, but now that I'm trying FreeBSD, here are some first impressions of the differences.
Reasons to Choose FreeBSD
Would you like clear, well-written user documentation, instead of curt citations of man pages, and faq entries? You want FreeBSD.
Would you like to experiment with hosting MS-Windows (or Linux, or another BSD, etc.) as a guest O.S. in a virtual machine, right out of the box? You probably want FreeBSD.
You have an older machine with only 1/2 gig of ram, and you think you should be able to run firefox without hitting the swap file? Free is the O.S. for you.
You have an older computer that runs at just under 1 gighz, and you think it's reasonable to expect an O.S. to deliver decent performance from that? You need FreeBSD
You've invested a lot of time switching from MS-Office to OpenOffice and you don't want to have to now learn the latest other OTHER office suite? Definitely, you want FreeBSD.
You're an experimenter who wants to install BSD on your Raspberry Pi? Most seem to agree, FreeBSD is a better fit for you.
Reasons to Choose OpenBSD
You think PF (Packet Filter) is a really cool piece of software and you want to run it? OpenBSD is for you.
And Now, for Something Completely Different
Are you a masochist who is excited by the idea of being beaten to a pulp, and left naked in the middle of the ethical, legal, and financial mine-field that is the GPL?. . . You want linux.