Now, you can't make your decision on where to sell an item totally on how much it will cost to list it or how much of a percentage the site will take on your sale. Cost certainly does come into your decision, but even if you get 100% of your selling price, that fact won't matter if no one sees your product and especially if the right type of customer doesn't see it. By "right type of customer," of course, I mean the person who is looking for such an item and might actually make a purchase. Someone looking for a car won't care a hoot if your homemade jewelry has some of the best designs out there, but someone looking for a Valentine's Day gift or a Mother's Day gift will be delighted to see what jewelry you have offered for sale.
Everyone knows that Amazon gets a lot of traffic, but we also know that people search Amazon for a wide variety of products. Still if I were selling books, I would probably think of Amazon first, as they have such a vast array of books for sale. Book sales will be more successful on a site such as Amazon where people are used to searching for books, but may also do well on sites that specialize exclusively on books, such as tomfolio, which caters especially to collectors. Where you look as a customer often depends on just what you are searching for, and the same thing is true for the seller as well.
If I were selling crafts, on the other hand, my first choice would be to sell on Etsy. Yes, Etsy may charge more for listing an item, but Etsy is also the first place a shopper would go if he or she were looking for a unique gift for a loved one. I know many people who search the Etsy site regularly for the unusual gift item that you just wouldn't see in a regular store. People who like to shop locally also seek local artisans by looking on the Etsy site. Etsy sends subscribers weekly suggestions by email based on themes, such as colors and holidays. I know I have purchased items on Etsy just because they looked interesting or unusual.
eBay is popular as a place to sell curios and antiques. In addition, anything you think would do well at an auction has potential on the eBay market.