Your favorite commercial community software? I have been fan of vBulletin and I run large community powered by VB4. It has its ups and downs, but in general gets things done. However, now that vBulletin talks about version 5 makes me think what is really going since we just kissed version 4.2. I have been thinking about alternatives so in my mind I can seriously think only about two other alternatives. This is just a small debate I do not intend to move from vBulletin (well not yet).
vBulletin 4 - Built on old system and even they know they messed by keeping old architecture. Now they just can't keep up with new stuff that other forums offer. However, VB has the best mods on internet and it keeps growing. Some of the best forums run on vBulletin including Sitepoint and Digital Point. It is secure and it has long history that I followed from the day one, but lately it has been under attack from XenForo community and some "individual" website like: http://vbtruth.com
XenForo - This is interesting project created by two Ex-vBulletin developers Kier Darby and Mike Sullivan. Guys went through a lot to keep their ideas fresh. Lots of courts lawyers and lawsuits from Internet Brands (company that owns vBulletin). Xenforo is built on Zend Framework (which is not my favorite) and it has promising future, but not yet there. They lack mods and driven community. Long way to go to achieve vBulletin.org popularity. I think it mostly lacks professional default look and other styles look more like free forums. Good ideas just not delivered properly.
IPB - Ok this is the software I have least experience with. Last time I tried it it had great skins and bad mod choices. They charge for most of the mods that vBulletin community offers for free. Every time I try to consider IPB something throws me off. Maybe just feeling that I can't shake off. Like a vBulletin ghost that chases me around when I look for other alternatives. However, if I do switch to other forum software it will probably be IPB, but we will see I am not in the rush there is long wait until we actually test new vBulletin 5.