I can only speak for myself, and their values in my world of writing.
This month's sales on Barnes & Noble (11 e-books) are about three times what I expect to sell on Amazon this year.
Amazon.com has been of no use to my in my quest for sales. They continually mess up covers, never think of changing a cover -it is a nightmare. You can never get the site to understand the basics of writing - too many Asians - who can't understand English. That is why I will only be using Draft2Digital in the future. D2D is always expanding their range. I may not see the benefit, but what works for some doesn't work for all.