1) Been with BSD/OS since it's inception. Great OS and good example to
follow. But BSD/OS was eventually killed and FreeBSD sort of inherited
it's legacy. Both follow the simplicity and good architecture models,
with FreeBSD improving on modularity.
2) The BSD license. Contrary to popular belief, it has brought a lot of
high quality development to FreeBSD.
3) Universal toolkit. It scales easily from the thinnest embedded
system, to various desktops to huge servers -- all with the same
familiar tools and environment.
Sure, for consumption there are "easier" systems, such as PC-BSD
(FreeBSD again), Ubuntu and, of course OS X. But there is no better
platform, or kit to build whatever you need around.