Which one do you like better? Please only vote if you have used *both* of them, or you have a really good reason for not using the other. Personally, I started looking into an alternative when one of my popular phpBB forums suddenly started getting targetted by a bunch of bots. When I went through the backend to impliment my own anti-bot scheme (and to add text link ads) I found out just how disgusting it is to work with :/. I uploaded SMF and used a converter so I could play around with it. So far it's pretty good, and the converter worked excellently.
There are many debates on which one is better. I have personally used SMF and I really liked it. But I see some themes made for phpBB are excellent. However, I still prefer SMF.
phpbb is the best in my opinion, although I wasn't really disappointed with smf either. So was phpbb last I checked