i vote for vBulletin/ its the best and you should select only those softwaer which should be useful future expansion purpose also.
Expression Engine has a forum module which can integrate with your site, if that is what you're expecting
i use to like vb but now i like phpbb was hard for me to use at first but now its easy. And its pretty darn good for free least you can have your forum grow and decide if you like it. where vb you have to buy it and your stuck with it and hear vb has a lot of bugs.
blah blah blah is the best because I use it and I'm biased. Repeat the above statement over and over again...that's the only real responses in this thread. Best is completely subjective to the user and his specific needs. Asking in a place like this is like asking what's the best tasting fruit.
If you want innovative simplicity in mind. Id highly recommend Vanilla 2. If you are looking are looking for the best traditional board then I will say go with myBB. I say mybb because everything there is user friendly, you can use plugins with just a few clicks and customize the theme and much more with a few minutes and clicks as well. If you are an expert with php, you can still do they indepth things you want to do.
Lies. This is patently false. Simple Machines owns the forum, it is provided to you as free. Check it out here: simplemachines.org/about/license.php
MyBB is open source under the GNU/GPL 3 license. http://wiki.mybboard.net/index.php/License SMF is NOT open source license certified by OSI. http://www.simplemachines.org/about/opensource.php Get your facts straight.