I think the iPhone5 was the perfect compromise between size and one handed function... I have a 6, not a 6 plus, and it is a fabulous piece of hardware, but one handed use is not nearly as comfortable or effective as the 5.
IN terms of comfort in the hand the original iPhone design was by far the most comfortable, the original iPhone/3/3gs designs were by far the most comfortable in the hand.
The larger screen is nice in the 6, but one handed operation is not nearly as nice. I personally can’t imagine the 6+, but like it or not the market is demanding these silly huge beasts.
There are rumors that they will be releasing a new phone that shares the same footprint as the 5 next year with updated specs... to fill in the lower end, that the 5C did.. not sure if its true or not, but if you like one handed operation, I would certainly consider it. As I said the 5 form factor was the perfect compromise to add size, and still allow comfortable 1 hand use.
I have a Iphone 5c. I love it. Perfect size and works great. Its running 8.1.2
Silly to you perhaps but in Asia they want large and mobile. It might be their only way (don't have much money) getting on line. They don't have a desktop at home with a 24" display///// They get it (internet) on the run.
Now ...... A relative who is pathetic on internet is loving her new large screen Samsung note that I see her typing the alphabet w a stylus