There is a lot of misconceptions out there about these two sellers and especially ebay. Many people think that eBay is just auctions and mostly used items. This is far from reality. eBay sells more new items than used items and that amount has continued to grow.
Amazon does not have an auction system like eBay so if you are looking for that platform then ebay will be the better choice. Amazon though is growing at a huge rate so there are more and more people using it so that is always nice as a seller and should be considered.
Between the two I have had good and bad experiences but on eBay their buyer and seller protection was better for me and handling things properly so I personally like them from a customer service standpoint. Not that Amazon has bad customer service but eBay's has just been better for me.
As for looking to earn income online and which would be best, that would depend on exactly what you want to do to make money. Do you want to sell physical goods, virtual/digital goods, services or are you just looking to market things?
How you are looking to make money online will help determine which is best out of these two options.
