I'm currently using phpbb 2 for my forums. I'm planning to upgrade it to phpbb3 soon. I think that if you want a free forum you should use phpbb.
Yes, VBulletin is a very professional bulletin board software system. The only problem I have with it though is that it is so expensive. It costs $160 to own and $85 to lease for a year. On the contrary though, there is Invision that is only $150 to own and the updates cost less (but VB's updates last a year and only cost $5 more). It is truely a toss up between the two for me. I have worked with both over the past few years, but to me it seems worth it to dish out a few more dollars for VBulletin. I never had to deal with their customer service though, has anybody here had a bad experience?
Yes, your right, vBulletin is the perfect script for the forum and most of the webmasters use that script, vBulletin provides your website with high-leveled protection. You don't have to worry that your forum can be hacked. One of the software benefits is that it makes it easy to import data. It means that you can easily move your message board data into vBulletin from other forums.