The iPhone, to me, is not really a phone anymore. It is a multimedia device and the largest screen possible that still fits comfortably in my pocket is what I want.
I want a nice crisp screen, large enough that I don't have to hold it right in front of my face with plenty of storage.
And for me, that is the 128GB iPhone 6Plus.
It has completely replaced my iPad mini, which I gifted to someone at christmas, and the main reason I still have my full size iPad is because I travel a lot and watching videos on a full sized iPad is much easier, for me than the phone on an airplane. That and I like reading books and magazines on the iPad Air.