The 2015 "king of e-readers", as stated on CNET, is the Amazon Kindle Voyage. It is the top-rated e-reader in several categories and by both professional and user reviews. The 2015 retail price for the Kindle Voyage in the United States starts at $199.
Along with the Amazon Kindle Voyage, the Amazon Kindle Paperwhite, which debuted in 2013, has the same integrated lighting scheme, but the processor speed is slower than in the Kindle Voyage. The Kindle Paperwhite is the "best overall e-reader value" on CNET and is priced at $99, making it a more affordable e-reader than the Kindle Voyage.