My personal list of ideal size/ergonomics for one-handed use.
Screen size too small -
Apple iPhone 5 (2012)
Apple iPhone 5s (2013)
Ideal range for me -
Motorola Moto G (2013)
Motorola Moto X (2013)
Sony Xperia Z1 Compact (2014)
Sony Xperia ZL (2013)
Sony Xperia ZR (2013)
Maximum limit range -
Apple iPhone 6? (2014)
Google Nexus 4 (2012)
Google Nexus 5 (2013)
HTC One (2013)
Huawei Ascend P6 (2013)
Lenovo S820 (2013)
LG Optimus G (2012)
LG G2 (2013)
Samsung Galaxy S III (2012)
Samsung Galaxy S4 (2013)
Sony Xperia Z (2013)
Over my limit -
Google Nexus 6? (2014)
HTC Butterfly S (2013)
HTC One (2014)
LG G3? (2014)
Lenovo P780 (2013)
Lenovo Vibe X (2013)
Samsung Galaxy S5 (2014)
Sony Xperia Z1 (2013)
Sony Xperia Z2? (2014)
^^^Generally all phablets like the Galaxy Notes, Galaxy Mega, Xperia Z Ultra, One max, Fonepad, Ascend Mate, K900, etc. Excluded BlackBerry and Nokia Lumias since I have zero interest in their OSes right now.
Seems like Motorola and Sony are the only Android OEM's who get it as I expect the Moto X2 and future Xperia Z2 Compact to be ideal to use one-handed. The iPhone 6 (rumored 4.8 inch screen) will probably fall under the maximum limit range unless they go edge to edge with the screen and then it might be the ideal range for me.
Yes, it seemed the iPhone 4/4s was the ideal size a few years ago. You can even make the same case for the iPhone 5/5s now with its elongated screen which bothered some early when reaching for the pull-down notification center. But once you go above 4.5 inches and use gesture swiping with an Android launcher, people who go back to a smaller screen will find it a bit too cramped with videos, games, browsing, and texting.
I always pictured if the Apple increased the screen to 4.7 inches, the iPhone would look similar to the Huawei Ascend P6 and a local branded smartphone here called the Starmobile Knight.
Moto X2 has solidified itself as my #1 pick this year even though Motorola will never popular like they once were and now are part of Lenovo. I'm also reconsidering the Huawei Ascend P6 or P7 just because their thinness makes it easier to wrap my hand around the phone. Also I find Huawei to have a better design language externally and internally than Lenovo. I like the very iPhone-esque look of their Emotion UI without the app drawer.
None of these bigger and successors to last year's flagships interest me as of late. The all-new HTC One is rumored to be 146mm tall, 70 mm wide, and weigh 160 grams with just a 2600 mAH battery capacity? A 300 mAh increase to last year's One and smaller to the Butterfly S? Size has become a turn-off from most of these recently announced flagships with 0.1 to 0.3 screen size increases that features on-screen buttons that also waste space.