I've been using phpBB for almost a decade now. While I really loved the 2.* versions, the current 3.* drive me insane. The software structure couldn't be more different and as a TechAdmin I had to almost start from square one again.
I've been flirting with vBulletin for a while but there are still too many security gaps in that software imo. For the moment, phpBB appears to be the safest software.
Maybe one day I'll take the last phpBB 2 edition, bring the security up to date, edit out a few bugs and in a few nice features and then use that one. Propably in 20 years when I get pensioned off *sigh* - before that, I won't have the time.