You may want to categorized the organizations into what purpose they will serve as you make your decision.
For instance; IVAA is viewed as a Trade Association for VA's (I think every business owner need to be a member of at least one Trade Association, some chose associations based on their niche, as Lily as indicated); I'm not sure I would view VANA, and VACOC, as a trade association, simply because (IMO) their most prized offering is the participation in their forums (this is what you would spend membership dollars (or time) on, VACOC does not charge-I don't think

).
With that said, I agree with what others have said, I get more information (and virtual relationships

) than I even know that I need from this FREE site! Therefore, I haven't committed as much time to other sites as I have to this one.
BTW, I am a member of IVAA

.