For me I'm a member of APS, USSS, UPSS, PSS and APC, as well as several on-line forums/groups.
I was a member of the PHS, but I wasn't getting their journals regularly and their website was woefully outdated with no one making an effort to update it. Also, as a U.S. only collector, the journals usually had one article relating to U.S. postal history with everything else involving other countries.
The last one I listed, APC, is the American Philatelic Congress. Basically, all you get is the annual Congress book as a member.