I hate to say it, but I will never forget the day I first stumbled upon PF.<p>Up to that point, setting up a router/firewall had been exceedingly painful, using Linux and iptables.<p>The syntax of pf.conf is beautiful. Somebody (I forgot who) once said that in order to write a rule set one needs to consult the (excellent) man page constantly, but once it is done, reading and <i>understanding</i> it takes no effort at all. As far as the "UI" goes, PF is so far ahead of anything I know of that most other metrics to judge a firewall / packet filter by seem to disappear.<p>Just to be clear: I have nothing against Linux, in fact most of my computers run Linux. But the syntax of pf.conf is just so sweet, once I tasted it, it spoiled me forever. And now iptables scripts look like something out of a Lovecraftian nightmare.