I found this hard to answer because some of the organizations require corporate membership and others require individual membership.

As a past executive of organizations of both types, I can tell you that the differences are tremendous.

Individual membership organizations tend to lean toward “networking”, career education, and social events. As important as advancing the standards of the industry and gaining knowledge, are those of improving career opportunities through better skills and either advancing within or outside the organization. I used to wince whenever an emplyee whom I reimbursed to join an individual member organization left because (s)he was found by someone at a networking party who was looking for someone for another job.

Corporate member organizations have other goals. Education is to improve the skills of the company through the individuals working for it, or benchmark the company skills against other companies. Improving standards tends to be for the good of the industry. The company signs off on the standards and practices and a company pledge of high standards must be weighted higher because it represents the way they want to do business.

So if I am the head of a company doing marketing research I would want the company to belong to an industry group whose standards are respected (e.g., CASRO, ARF and perhaps an international equivalent.) For me personally (I’m no longer concerned about career advancement,) I would gravitate to a group of senior researchers who discuss issues and research approaches that keep me up-to-date or ahead of the curve (AMA, MRA, ESOMAR) or one of the several “rump” groups of researchers (based on invitation) meeting in nice places with intensive programs of discussions and practices.