To reiterate what we've all said before, there are all kinds of users.
For instance, a petite girl with small hands... you can be quick to say she would prefer a smaller form factor, but she may have a purse to carry a larger device.
Or a man with very large hands... may be more comfortable using a 5.5" phone with one hand... but that doesn't mean it's going to fit in his jeans pocket.
There will always be something for everyone.
I've used a samsung gS3 among other phones.... and I cannot use it with one hand without dropping it. I've gotten pretty good, but it's very difficult for my hands. It's only a 4.7 (or 5. for S4).
Part of this is also shape of edges, and where the weight of the device is located. Some phones are heavier on the bottom, some are heavier on top, some have rounded edges, some have sharper edges, etc.
...and where navigation buttons are located.