If you need to go with vBulletin, then I'd suggest Drupal vB over the other choices. vbDrupal is a "fork" of the whole Drupal project, which means they had to edit the Drupal core in order to integrate it more fully with vBulletin. This means the Drupal community will have trouble helping you with any problems (so for support you may be largely limited only to the small vbDrupal community). Though they have a track record of releasing security patches within a day or less after they come out for the real Drupal, they are far behind in keeping up with the major version (they are still on Drupal 5).
So far as Drupaltin... it was a promising attempt, but has pretty much died.
Drupal vB probably has the least significant level of integration between the two systems, but it does so as just a simple Drupal module. It provides the most important aspect, which is bridging the user accounts of both systems. Drupal vB is likely to remain well taken care of and upgraded to future versions, as it is developed by several highly-respected Drupal contributors (sun and rszrama, the latter of which is the developer of one of Drupal's 2 main e-commerce modules, Ubercart).
If you don't need vBulletin, then consider one of the phpBB bridge options, as they are likely to offer more integration, since phpBB is open source. Here's a listing of all modules that have anything to do with phpBB: http://drupal.org/search/node/type%3Aproject_project+phpbb (the one that looks most promising to me is phpBBforum module)
All that said, also consider sticking with the Drupal core forum, paired with the [Advanced Forum module, which helps automatically make the forum look/behave more like vB or phpBB, and automatically enables extra features depending on other forum-related modules you have installed in Drupal. I originally planned to switch my site to Drupal and use a vBulletin bridge/module... but since then I've personally changed my mind and will be going with the core forum (especially since it's much easier to style/theme however you want now in Drupal 6 and/or with Advanced Forum). The forum theme is a bit more simple than you'd probably want (you can customize yours however you like), but here's one example of a [URL="http://socnet.shellmultimedia.com/forum"]Drupal Advanced Forum. Here's a nicely styled Drupal forum (I believe it is just core forum, not Advanced Forum): http://dc2009.drupalcon.org/forum](http://drupal.org/project/advanced_forum)
Good luck with your site