It all depends on how you structure your hubs, and the goals that you have in mind for each hub you create. Like it or not, if you want to be successful with any internet content, you have to learn to be a marketer.
For me, Amazon has been my best earner, namely because I structure my hubs to favor them. I take extra time to find the products that are really relevant to someone who would find the article useful, and I give them a prominent place on each hub. In articles that discuss specific products, I will point people to the right side of my page where they can find the link to that product. I do earn some from eBay, but my eBay capsule is a footnote more than anything. I can't do the same kind of customized approach that I can with Amazon since eBay auctions are always changing, so I can never guarantee just how relevant those listings will be. I don't like promoting something that might not be of use to my readers, so I spend very little time or space on the eBay capsule.