I used the 6 for a few hours before realising it just wasn't for me. Gave it back the next day and bought a 5S instead. The 6 was just too uncomfortable to use.
What's the point of a bigger screen if it compromises usability? Try reaching your thumb into the top left corner of the screen (as you frequently have to on iOS), it just doesn't work without readjusting your grip and making it easy to slip out of your grasp.
The very fact that you need a feature called "Reachability" says it all. It's practically admitting the screen is too big for conventional use! Such an inelegant solution and Apple would never have offered such big phones if they didn't feel the need to catch up to Samsung.
As I said, I don't see understand the fascination with a huge screen in your pocket if you can't use it comfortably. I think the 5S is the perfect phone and am thrilled with it. This "which smartphone has the biggest screen!!11" pi55ing competition has ruined the iPhone line IMO.