Especially now, IPB2.0 is not free like its previous 1.3 was. A lot of sites will either be switching to IPB2, or vB. As far as I know, if I were to pay for a board I would go with vBulletin simply because of its pretty much bullet-proof rep. phpBB has too many problems, I wouldn't even consider it anymore. Its also taken them years to come out with their new version.