Ok, since there are not too many replies I would like to share with you the tests I have.
In general: I have meningitis support forum for kids and their parents. Since I looked a lot for decent group support chatroom for community chat, including the wordpress default one (which was really minimal and created a huge load on my hosting server).
I choose the RumbleTalk for my organization. The main benefit for me was the mobile chat orientation.
During my 7 years of running this activity, we used to have Java based chat room, but many had problems to connect as they need java installed (which mean less and less people this days).
We also tried flash chatrooms, but again it is not that friendly for mobiles.
So overall, I think the options are not that great with respect to users integration, but RumbleTalk is a decent choice (my 2 cents opinion).