That question can be answered in one way if you are just curious about how
the different BSD's vary.  Presumably, though, you are interested in using
a BSD as a practical choice for your ISP.  Yes?

Have you used any of the BSD's?  Ideally, you should be able to readily
adapt between the BSD's (or other UNIX-like systems) without much
difficulty.  But, it's that mucvh less to worry about if you already are
comfortable administrating the system that you'll use.

Do you know what hardware you'll use?  If yes, then that may narrow your
choices for you.  If you don't know what hardware you'll use, then going
with NetBSD is most likely to keep your options open.  (NetBSD probably
supports more hardware platforms than any other OS.)

You mentioned only free BSD's (I think that BSD Lite is technically free,
but is more of historic than practical interest now).  Would you consider
BSD/OS, a commercial BSD from BSDi?  Or contact Wasabi for commercial
support for NetBSD?

How important are things like uptime to you?  Is this a strictly
enumerable, practical decision, or would philosophy of the development
(affecting future work) affect you?  Size of the user base (too large can
get noisy and crowded; too small can leave you feeling isolated)?  
Available applications?  (Which applications?  See
ftp://ftp.netbsd.org/pub/NetBSD/packages/pkgsrc/README.html for the
packages availble for NetBSD, by category.)

See also, for a list of NetBSD features:

 http://www.netbsd.org/Misc/features.html

...I imagine that the other BSD's have similar information on their
web-sites if you go look.

Good luck in making your decision.


  "I probably don't know what I'm talking about." --rauch@eecs.ukans.edu