I agree that bigger is not always better but my smartphone is more than only a phone. I actually use it for other uses a lot more than I use it as a phone so the current screen is too small for me. I still think around 4" is a good compromise in size. I can't speak for anyone else, but 4" is still small enough for me to use with one hand but it offers a larger screen.

I also don't wear skin tight pants so it's not really an issue for me to fit it in my pockets. Ideally it would be best if we got to choose between two sizes. If Apple kept the resolution ratios the same then apps makers would only have to make their apps fit on the larger iPhone and then everything can be easily downscaled for the smaller iPhone.