[ForgotenDynasty]

ive had the opportunity to use both i started with phpbb then when i was offered an owned vbulletin for 50 bucks I couldn't pass it up.

Basicly heres what ive noticed

vbulletin
Pros:
Alot of out of the box features such as quickreply quick edit and overall better look
Easy to install mods Simply just upload the xml file
And your site gets an overall better reputation when it shows that you have actually put money in to your site.
Easier to moderate (moderator controls are more accessible.)

Cons:
Cost money (not just the board with its self is 200$ new but if you want VbSEO you tack on 150 if you want a skin your talking around 40) in the end your talking 400$ to just get your site presentable.
ACP isn't as User Friendly as PhpBB (Its not that its more confusing its just that theirs so many features its almost overwhelming IE it takes forever to set permissions where as Phpbb is just a dropdown box)

PHPbb:
Pros:
Free (Seo and all mods are)
ACP is very user friendly
Since you install the mods manually its alot easier to customize it when you see the accuall code behind it.

Cons:
People don't give you as much respect when they see a free board
Less features
Mods are a pain to install
NO out of the box features
and not only are the mods hard to install their are always like 5 different versions of each mod so if you want to just try each your talking 6 hours where as Vbulletin you just upload the XML file if you don't like it remove it and try the next.