Talking about theoretical devices, I did some number crunching and here are my thoughts.

The thickness (or thinness) of a device is important.
The thinnest I would want my phone would be 7mm's.
The thickest I would want it would be 9mm's.
However, if it is a qwerty/gamepad device like the Xperia Play, Moto Droid, Jolla OtherHalf... then I could accept it as 13.5mm's.

The screen size is also important.
I've got large hands, enough to palm a basketball. After my hand's size you get Pro-Basketballers and Andre the Giants. I don't think there's a market for that :P
So for me (and the majority) the maximum screen size is going to be 5.7 inches.
The minimum is going to be 5.2 inches.
For qwerty/gamepad devices this is of course subject to phone's dimensions.

Now bezels are really important for me.
I can't have a lot of it, but I do need a decent amount.
This amount is for holding the device from the sides and inserting front-speakers (it is NOT for logos or lame buttons!).
With that said the minimum Screen to Bezel ratio should be 75%.
And the maximum should be 80%.
(The Sharp Aquos XX-302Sh has a StB ratio of 81%)

1) So the largest phone I could deal with is going to be:
5.7inches screen, 75% StB, and 9mm thick.
Doing the maths it yields a device that's 152 x 79 x 9 mm (108,000mm3). That's basically the size of the Note 3. No wonder I like it a lot.


2) And the smallest phone I could deal with is going to be:
5.2inches screen, 80% StB, and 7mm thin.
Doing the maths it yields a device that's 139 x 67 x 7 mm (65,000mm3). That's the size of the iPhone 6 which has a puny 4.7inch display.

3) And the ideal OtherHalf device I could deal with is going to be:
110,000m3 dimension, 12.5mm2 thickness, 80% StB ratio.
That leaves us with a good 8,800mm2 for the front panel.
Give it (at least) 2mm of bezel to either side of the display.
We factor in that it is a 16:9 screen.
**tricky arithmetics here**
We end up with a device with a nice 136 x 65 x 12.5mm size. About the same footprint as the HTC One (M7).
That means its screen size is a modest 4.9 inches (sweet).


If you gave me the option between the three, I would honestly be lost.
Yes, I love the large screen size that helps immensely with in-car GPS.
Yes, I want the compact size of the second device that can slip in/out of my pocket and do cartwheels in my hand.
Yes, I appreciate the physical input from the 3rd device.

edit: Please Tell Me Which Device You Would Prefer From This Choice Of #1 #2 and #3 and Please State Why. Thank You!!