I think it's safe to say that by now there is no exact science of prediction here. I get the sense that exclusive vs independent has more to do with your worldview, personality and workflow than anything else.
I "Like" multiple agencies, simply because I naturally lean towards avoiding single baskets of eggs. I can't prove that it's better, it's just better for me, quite honestly. And I have my own little site that earns even less than what I do at Canstock, but who cares if I dig it?