Agent or Agency

What's more important the agent or the agency? This past few weeks, many actors, writers and producers found themselves swaying under new banners in order to either follow and agent to live the dream of being with a big name agency. Gersh agents leaving for CAA, CAA agents leaving for WME...no matter what the directional pull, one of the toughest decisions would have to be who to roll heads with. So if the power agent or spiritual head, "Jerry Maguire" of the company decides to leave, should an actor remain loyal to the agent or stick with the brand label he wants on the back of his resume?