As both a long-time forum user and forum administrator, these are my thoughts on vBulletin.
vBulletin 3.x
Certified 'hood classic. The worst you'll hear people, including me, say about vB3 is that it's now pretty damn old. To be quite honest, if it wasn't for security, I don't think vB3's age would be nearly the problem that some people are making it out to be. But... Sadly, security on any public-facing website IS a problem, and though it is true that it is very usually HIGHLY unlikely that anyone's going to care enough to hack any small vB3 forum, it's best to not dance with that particular devil there and just use something more secure.
vBulletin 4.x
Was pretty bad during the 4.0 days I hear due to how buggy it was, but I'm heavily biased in favor of this version, especially as a user, since I was a user of vBulletin when it was at 4.1.x and later and was actually fixed and stable. 4.2.x specifically holds a special place in my heart not just due to the lovely nostalgia, but also due to how ridiculously powerful the software was and how good-looking and intuitive it was at the same time. Once again though... vB4 is definitely in the same boat as vB3 in that it is getting too old to be desirable to run on a public-facing website anymore due to... Say it with me... Security.
vBulletin 5.x/6.x
This was after the falling out with the afterwards-christened XenForo team, and boy oh boy, was it evident why they left Internet Brands, both legally-wise and software-wise. I think it's pretty clear to many people here that the entire vBulletin suite took a dump after the original XF team left and vB5 came out later. So damn buggy... I might admit that vBulletin 5.x perhaps had some redeeming features to it, but even if vB5 AND vB6 were absolutely perfect, the management at Internet Brands was and is so bad that, in my mind, it wouldn't and still doesn't matter. Their terrible attitude and their terrible decisions have been slowly tanking the company and the community since. vB6 just seems to be a resounding more-of-the-same, and not in a good way, and now I hear vBulletin.org is shutting down. I mean, what more can I say? This crap speaks for itself.
So no, I don't think I will be switching to vB6 anytime soon.
