Doesn't the Z3 Compact have a 4.6 inch screen?
What other manufacturers have a flagship smartphone with a 4 inch screen?
It's is 4.6" not so big of a deferents if any to the iPhone 6 4.7"
I didn't make this clear in my original post, but I don't care about screen size, I care about one-handed usability. Admittedly, I haven't held a Z3 Compact in person, but, for example, I've tried a 1st gen Moto X, which has a 4.7" screen but it's completely usable with one hand in the same way an iPhone 5S is. I've heard the Z3 Compact is similar in that regard.
The problem with the iPhone 6 is the height that the home button requires and to a lesser extent, the bezels on the side. With Android, you can have soft buttons, so the space below the screen can be minimized. I suppose Apple could tweak the 4.7" iPhone to be smaller but still use the same screen size, and that would help, but it's very unlikely we'll see a design change until 2016.
Of course, with all of this I'm talking about my hands specifically. Though I'm 6'3" and have medium sized hands (I play most guitar chords with ease, for example). I can't reach the opposite corner of the iPhone screen with my thumb, at least not without repositioning it in such a way where I can't press the home button without repositioning it again.
I could live with the iPhone 6, especially if I get my other issues resolved, but I'm just nowhere near as satisfied as I have been with past models, and more open to buying a competing product than I've ever been.