Guneyd said:
Invision Power Board is the way to go... vBulletin has gone downhill (v3 was great.. v4 is a trainwreck).
vBulletin got new owners and some of the developers didn't agree with the new direction the software was taking and decided to start xenforo.
Invision Power Board on the other hand, has only continued to improve and improve. They also listen to the customers for new additions.
Yes, vBulletin 3 was and still is great.
vBulletin 4 in my opinion is better, but don't care for their "CMS" In fact you could buy the 'Cheaper Solution' and download a 'Free Solution' from the Mods Section or
http://www.vbadvanced.com/products.php?s=fd82da0066027dc3583db94d9c02255c&do=productinfo&productid=4 - This one works great, I think it supports v4.
vBulletin did get 'New Owners' and I've heard that story about XenForo, In fact here's part of the wiki article.
One of the developers of XenForo, Kier Darby originally served as a lead developer for the community platform vBulletin. The original owner of the software, Jelsoft, was acquired by the American new media company Internet Brands in 2007. Disagreements between the lead developers and the new management over matters involving the next big release of vBulletin, version 4.0 (including a rejection of their desire to make 4.0 a complete rewrite of the platform as opposed to Internet Brands preferring the use of agile development) led most of the original vBulletin developers to step down from employment at Internet Brands in 2009.
Source: http://en.wikipedia.org/wiki/XenForo
Too be honest I don't blame them for quitting vBulletin, I would of probably done the same if I was in that position, wonder if vBulletin was a complete re-write or a built upon the vBulletin 3 product...at any rate, This caused XenForo to be born and it's a good forum script and totally recommend either of them.
As Rodolfo mentioned, He's not inclined to use 'Open Source' if he were to changed forums because lack of support or technically none at all and have to rely on the community.
Whereas he also mentioned money isn't an issue and having vBulletin or XenForo in its placed would be a significant upgrade as I've more less own both licenses and even considering buying another for another domain.
vBulletin 4.x License - $195 - 1 Year (Updates Included)
vBulletin Renewal License - $175 (Updates Included)
Source: From website, logged into my account I own.
XenForo 1.x License - $140 - 1 Year (Updates Included)
XenForo Renewal License - $40 - 1 Year (Updates Included)
Source: From website, logged into the account I manage.
IP.Board 3 - $175 (6 months software upgrades/support)
IP.Board 3 Renewal - Not sure, but Optional 6 month renewal: $25 for Support
Source: From website, can't log in to confirm renewal rate as I don't own a license.
I'm inclined that XenForo is a good choice of even vBulletin, but either way I'll be happy with either forum you choose.
After knowing this information, maybe it will advise you choose a good forum script.
Regards