About a year ago we asked you what was the ideal screen screen size and the answer was "between 5-inch and 5.3-inch". Will the answer be the same this year? Last year we pointed out the growth trend in most product lines. For example, the original iPhone had a 3.5" screen, the iPhone 6 Plus went up to 5.5". That trend is still going, though most recently we're noticing a shift in it - screens are growing taller, but not wider. The LG G6 and Samsung Galaxy S8 have bigger screens than their predecessors with an aspect ratio wider than 16:9. We've always said that width is the limiting...
Source: http://www.gsmarena.com/weekly_poll_what_is_the_ideal_screen_size-news-24995.php