Mark,
I just went through the "research learning curve" on just this topic... which is the best BB. Of course how do you define the best. What are youe exact needs, etc.
I am building a site for Honda automotive techs. It will have forums, chat, news, and online training available by subscription. My original plans were for the site to be a traditional framed html site with a BB that would open in the main frame when they clicked on "Forum". All the other site functionality would be built with html pages. So I was looking for a BB as an add on to a html site.
I knew I wanted to offer my training modules on a subscription basis. So my first quest was to choose a good subscription/membership script to control access to this information. After pretty exhaustive research on this, I decided to use aMember Pro Membership script to control access to my training modules.
I then saw where they offered a plug-in for many BBs so you could sell access to specific forums for specific amounts of time. This got my attention. It seemed like a good option to have, in addition to controlling access to specific folders for specific amounts of time. I then decided to use subscription controlled forums to deliver all my traning. The simple explanation is that I will put links to PDF files in the forums. As long as they have a paid subscription they have access to the links (and yes there will be provisions so they will not be able to visit the link after their subscription expires).
I have 10 training modules that a customer will be able to subscribe to. Basically $20 buys you 60 days access to a module. $100 gets you access to all 10 for 6 months. I needed to be able to have a member subscribe to any combination. Such as subscribe to Module A today, subscribe to Module b in 2 weeks, etc. As it turned out Threads was the only BB that allows a member to belong to an unlimted number of groups, which is what you need to do this.
So that took vBulliten and Invision Power Board off the table. When I started taking a close look at Threads it was apparent I was doing the right thing. Threads has plenty of horsepower and features, yet is not so complicated that it takes weeks to master. Take the time to visit vBulliten and IVB and read their Admin manuals. It will make your head explode after an hour or two... LOL
In my humble opinion, some of the high end BBs have become way too feature laden and complicated. You want a headache, try to read and try to understand the "skinning" process on either of these two boards.
I had decided I was going to use Threads for the BB part of my site and to deliver information based on subscriptions. Everything else way going to be html. Then I found this site and saw how you could let threads drive an entire site with some of the mods and add ons developed from this gang. I do not think you will find such a large and vibrant independent suport group like this one with any other BB.
Now it looks like Threads will vitually drive my entire site. The content of the site will built up by visitors contributions. I will provide a vehicle for them to share service information (for free) and sell them access to training when and if they want it.
In my book Threads was the best choice for me.
Hope this helps!