Invision Board is 1000000000% better than vB2 (with respect to code quality and performance). (nearly everything is better than vB2) However, with the coming of vB3, Jelsoft pulled the gap and now both of them are nearly neck and neck. Both have unique features the other doesn't. I personally would be happy using either.

phpBB isn't "riddled with security flaws." It did have a few major flaws that were quickly fixed and the developers are constantly tackling any issues that arise. The reason that many hosts canned phpBB was due to a vulnerability with awstats as well as a PEAR bug in php, both of which got blamed on phpBB. Also, many phpBB users and hosts didn't install the security updates when they came out. If they had, then less people would have been exploited.

phpBB3 Olympus will certainly give IPB and vB a run for their money, especially since Olympus is free.