After trying to integrate a few of them into vb, I decided that best one is
Real Chat but it would require you to be on dedicated server and it is pricey either. However it integrates vb better than all other the scripts I have had experience.
On the other hand in such a integration everything would not be possible as the integrating scripts are from different worlds: VB is PHP and Real Chat (or any other good chat script) is Java. So you can not make all dreams possible while combining a chat script with your forum but Real Chat is flexible to make most of your requests come true.