Smart phones have a come a long way since I started covering them professionally back in 2009 they have a ton of new features, GPS, 41mp cameras, fingerprint sensors, heart-rate monitors, etc... They have also in increased in size perhaps a little too much even.
When the HTC Titan came out it was well...HUGE at the time. I remember opening the box to it's massive 4.7 inch screen. That's right massive! People made fun of me for how large my phone was and asked how it was even useful at that size. Now devices that are under five inches are "mini" devices. Which begs the question what is the idea smartphone size?
Up until two weeks ago I'd be firmly in the 5.7 inch plus camp. I mean honestly how often do you use your smartphone as phone? Five percent of the time? Most of the time it's more of tablet. Playing games, texting, watching Netflix, showing of pictures to your friends, etc... All of this stuff is best done on a larger screen.
However I recently went back to my Lumia 1020 from a six inch device and I find the 4.5 inch screen to be more useful to me. Even with my small hands most of the screen is reachable and I am using it one handed all of the time now. It pockets in/out like a breeze and feels more natural in use. This isn't saying I don't miss my large phablet device sometimes because I do however I have the tradeoff isn't worth it anymore.
So what's the correct screen size? That depends on how you use your device but I think ASUS has the answer to this problem and no one is simply paying attention to it.
Asus Padfone line is the answer. A 4.5 to 5 inch device that docks into a 7 to 9 inch tablet. Yes please!! This allows it to be portable enough as a phone yet relax at home like a tablet. I have no idea why others have not jumped on this form factor. The hardware itself if not great, a mid-range at best however the idea is sound. Rumor has this device getting refreshed in a Android and a Windows Mobile version. If indeed the update version is Windows based I will be first in line.