Well I only use this forum and have so for almost 3 years now. I chexk out others every now and then but they seem amature and chaotic sometimes. For me this setup is easy to navigate plus Sakara keeps me busy with posts so I don't really need to go anywhere else.
You have to know what you don't know.
This is the only forum that I've been a member of. I've been here since 2006. I couldnt speak to the number of MMA forum members but you can find out how many are here. Only other site I visit is Sherdog, and I never go in the forum, just read the articles and use their fight finder.