Screen size, resolution and quality are some of the most important features to consider when choosing a smartphone.
Apple iPhone 6s Plus's 24 IPS and Apple iPhone 7 Plus's IPS screen have exactly the same LCD size of 5.5" so we don't have a winner here.
Besides comparing the LCD sizes, another specs that we find useful to compare is the ratio of screen area to total surface area of the phone (screen area/total surface area).
Apple iPhone 6s Plus and Apple iPhone 7 Plus have exactly the same display coverage of 70%- so we don't have a winner here.
Screen size is only one side of the story, resolution is as important in most cases.
Apple iPhone 6s Plus and Apple iPhone 7 Plus have exactly the same pixel density -401ppi- so we don't have a winner here.