I am looking for suggestions for which Groups Modules would work best for my site.  I would like to allow users(group admins) to create their own group.  I also want the group to be open to the public, but have a tab or some section in the groups to allow for private chats that the group admin would control who has access to the private sections.

I am currently looking at VivoGroups, I like the options it has, but havent found where i could make private sections yet.  Anyone know where it may be?  Are there any other groups you would recommend?  Free? Paid versions?

Thanks for your time