I'm heavily considering going from an iPhone 6 Plus to iPhone 6S because of its size. Don't get me wrong: both the display and battery life are amazing and I have no trouble whatsoever to use it with one hand. But, in my case, it usually 'only just fits' in my pockets.
That's not really a problem if you are doing something static, but as soon as you start to become more active (for example, if you go cycling), it's becoming a problem because you'll feel pressure.
The 6 Plus, honestly in my opinion, is just ever so slightly too wide and ever so slightly too tall. If they manage to reduce the bezels with the iPhone 7, the device will be a lot more mobile I believe.
Again, display and battery life are awesome.