1) When it comes to maintanance it's a matter of taste and preference and it's very subjective view what is better or worse. It haves nothing to do with "better" (something that BSD guys fail to understand all the time). It's just a matter of preferences. From my standpoint, it's highly debatable if it's "easier to maintain". Look, when I want to catch some data packet with known data at known offset, in Linux there is module which would do exactly that for me. With reasonable simple commands. Now your turn. I've seen how BSD guys implement things like this in BPF assembly language. Because there was no other ways to do so. And it has been a clear winner in "unobvious firewall rules contest" . OTOH in Linux you can have string matching rule in more or less human readable form. And features like this is what I would expect from more or less advanced firewall for sure.
2) Netfilter/iptables also would not make any discounts for these "wanna be a cool firewall". You see, there are really powerful and cool features. Say, ipset could ban a huge numbers of IPs without getting horribly slow. And it's better in terms of features than anything BSDs could offer.
but openbsd is not so good something like MySQL, postgres, performance in Linux is better for this, people here should have to recognize advantages of both systems and stop this stupid discussion.