See quite a few articles about the Plus being way too big. But my main reason for keeping the plus is battery life. I love the form factor of the iphone 6. Good compromise keeping it the size and increasing screen size to 4.7. But it's only marginally better than the 5S (in my opinion)
This author shares the same opinion.
http://www.cnet.com/news/my-only-iphone-6-regret-is-battery-life/
This author shares the same opinion.
http://www.cnet.com/news/my-only-iphone-6-regret-is-battery-life/