Slimmer design or larger battery?

(I presume that batteries can be custom-designed to be vertically or horizontally larger. Pls correct me if I am wrong?)

I love the thin slim sexy two-tone design of my iPhone 5. I just love it. I am sure many of you do as well.

But I don't love its battery life. It's less than acceptable. ( at least for me) I am sure many of you agree with me on this, again.

Still, I am not sure if I would have preferred an iPhone 5 with everything it is now but in a thicker design(9.3mm, like 4S and 4) with a bigger battery.

How about you? Design or function?