It really depends on your requirements.
http://www.phpbb-portal.com/ gives you a pretty basic setup with a forum and a few portal items.
http://postnuke.com/ has quite a few more modules which they call blocks or plugins depending on the functionality.
http://community.postnuke.com/module...play-pid-7.htm
If you are looking for more of an announcement/discussion community site, I would probably lean towards phpbb/phpbb-portal.
If you wanted something more dynamic with event scheduling, local temperature, preferences, user picture uploads (i.e. community events, photo galleries, etc), I would probably lean towards postnuke. (Postnuke has a module that embeds phpbb)
Either way, your forum will be based on phpbb, which can be pretty easily migrated to vbulletin. As for the CMS portion of either setup, vbPortal is a bit more difficult to import data into.