For me Altnews gave me the guts to start this on aus-city and I thank them for giving me the kick to do this.
As for more forums the more the better.
But whats counts the most today is getting the word out + the ease of using the forum and that probably counts the most on who goes where.
I have been on forums since the internet started and trust me some are a pain in the arse to use and that alone sends you elsewhere.