Ok the reasons why I bought the 6 plus specifically were because of the larger display, the 1080p resolution, that it was available in 128GB of storage and the excellent battery life.
I came from android and had been using large screened phones with high resolution, expandable storage and removable batteries since the original galaxy note in 2012. I left the iPhone in 2012 primarily because I wanted a high resolution phablet with expandable storage.
So to switch back to the iPhone it had to have a large enough display, with at least 1080p resolution and enough internal storage and battery life to offset the fact that the memory couldn't be expanded and the battery was not removable.
I've had every plus model (6+, 6S+ and 7+).