Nearly 20% of U.S. broadband households owned at least one streaming media player last year, according to research firm Parks Associates. Roku was the market leader, accounting for over a third of new device sales, followed by the Google Chromecast, Amazon Fire TV, and Apple TV -- in that order.

Amazon launched the Fire TV last April, but Apple didn't update the Apple TV last year -- which possibly explains why the latter slipped to fourth place. Since both companies launched new set-top boxes this year, the 2015 sales figures should give us a clearer idea of which device is more popular. 

From the article "Amazon Strikes Back at Apple With the New Fire TV" by Leo Sun.