Why IPB? Flexible Permissions
Control exactly who can access what, with incredible precision. Encourage Interaction
Drive user interaction with profiles, statuses, personal conversations & more. Painless Moderation
A wealth of moderator tools make it easy to deal with troublemakers. Fully Brandable
Powerful customization tools enable you to entirely rebrand IP.Board. Secure
We work hard to ensure IP.Board keeps your users & data secure. Developer Friendly
Extend built-in capabilities using IP.Board's development toolset.
Those are just some key points to why ipb is a lot better than other forum software, like phpBB and vBulletin. The only person who can choose is you, but after my research when I was in your position I went with IPB, and I do not look back. I would strongly recommend you becoming a IPS customer rather than other software.
Check out this page http://www.invisionpower.com/products/board/features/
To also see if its right for you , you can check out the product demo. http://www.invisionpower.com/suite/demo.php
Hope this helps you come to a conclusion.