The one thing I was convinced that I would never get used to is the larger size. The iPhone 6 is bigger, and it has forced me to change the way I hold it, but I have adapted over time.
The benefits of the bigger screen go along way to make up for the inconvenience of the awkwardness trying to use the iPhone 6 with one hand(as a commuter this happens a lot, for those who use their phone with both hands because they have a luxury of a seat on the way to work this will be less of a concern).
I’ve adapted to holding the iPhone in such a way that I can hold it with my fingers and gently move it around in and let it slip into a different position in order to reach the corners. I don’t ever find myself using Apple’s Reachability system(where you can double tap to bring the top to the screen down) probably because it just feels like an extra step, and extra steps take time.