What is BSD?
NetBSD is the highly portable
flavour of BSD - if a box can't run BSD; it's not a computer.
Okay, this is not really true, but concerning 32bit and better
hardware this is almost true. NetBSD often is the only possibility
of getting some piece of hardware to work when you don't have
the original OS.
Have a look at the impressive list
of supported hardware architectures.
OpenBSD is another flavour
of BSD with its main focus set to security. The distributions
are really well chosen pieces of software and there are really
only few security holes if any at all in the standard installation
(according to their webpage, only one remote hole in the default
install, in more than 7 years). So this might be your best choice
for setting up a server.
OpenBSD is also available on various hardware platforms, but
the list of supported
architectures is not that long as in NetBSD
FreeBSD is the third flavour
in the BSD family with its focus set to usability and current
software versions. This would be the best choice for installing
BSD on a desktop.
FreeBSD has the smallest list
of supported platforms, but the most important ones are supported.