I always wander through three forums: HKN, FSM and ARC, and exactly in that order.
I have the impression that HKN has just a little more on the civil helo-side, and being a modeller of civil kits, I like that. The FSM threads can be divided in chapters AH1, UH1, UH60, CH53, AH64 and CH47 and only occasionally something else shows up.
What I like best on HKN though, is ofcourse the HKN-"magazine" with all the latest helicopter kit news. Although I should not bite the hand that feeds me: FSM as a magazine imho is not really helicopter oriented.
HKN however does indeed seem to have a "quiter" forum: not as many posts as on FSM, and posts don't get as long as the ones on FSM.
Whatever: the more modelling forums, the more fun!
Cheers!
Gertjan