What is the best forum software?

If your talking paid software +1 for both Xenforo and Vbulletin. MyBB is the best free one by far though.

 

If all you want is a forum, then vBulletin (paid) and phpbb (free) are the best options, in my view. If you want an integrated website/foum/community, then Joomla + Kunena + JomSocial (optional) is a good combination that integrates well together.

 

MyBB is good for free. And IMO I think XenForo is good for paid. I've used it for a while and it seems to be working fine. Loads of plugins are available too.

 

There are lots of options available depending on what you want to achieve with the site. The best one currently available with the best security, more advanced and looks the best is VB Forums. However, along with ipb these are for those who can afford it. You have to pay for the license which can only be used for one site but its currently the best thing out there with tons of skins available. SMF or phpbb is also available but doesn't have the advanced feel or options that come with the others. Its really a personal choice.

 

Free = mybb or phpbb
Paid = vbulletin