There are three helicopter specific modeling forums I have been part of since their inception. Not to offend anyone here but I have to say HKN is my favorite. Especially when I'm too busy to regularly visit. Here are a few reasons:
International diversity (in terms of aircraft, products, and contributors)
Nice mix of civil and military
Posters use real names and email addresses
More mature (because of above?)
Accurate answers (because of above?)
No post individual counter or rating system - posting BS doesn't earn you rank
More on topic posts (because of above?)
Most people only ask for help after the have exhausted the search function (not the same old question over and over)
That's my two cents. Not trying to diss this site or the fine people on here - just telling you why I like HKN. It's funny becasue if even they don't use their real name here or on ARC I can still tell (from personality, temper, or build subject) who certain people they frequent all three sites.