I would take a 4.3-4.5 inch iPhone.
After using the android mini tablets (that's what i call my android smartphones, and that's what they look to me), i am not very happy with huge screens.
The thing is, watching videos is not as much fun even on a 5 inch screen as on a 7-10 inch screen. If i am watching something in a pinch, even a 4 inch screen is fine in that case, the 5 inch does not make it much better for me.
Reading big PDFs isn't as awesome on a 5-5.5 inch screen as reading them on 7-10 inch screen sizes. I only keep Moonreader+ on my GS4 because of that odd small one-two page PDF that i might need to glance on, but in that case an iPhone did fine too in the past. Again not so great for my needs.
Reading websites even on a 5 inch screen for long periods isn't as much fun as on a 7-10 inch screen, again for me at least. I use feedly on GS4 not because i like to read long news articles, but because it has that awesome title only view that can show me all news in a couple pages which i can skim through. If something is very important, i will send that link to pocket, open it in my laptop or PC or N7, and read it there.
And we see where we are going on and on...
However, for general smartphone stuff, i don't need such a huge screen. Music management, alarms, note taking, reminders, communication, social, emails, you name it, all work fine on a 4-4.5 inch screen, again at least for me.
This is why i liked the moto X, as though it was 4.7 inch the build was very ergonomic. I hate this huge screen trend. Ideally in future i would rather have technology that allowed a 4 inch smartphone to stretch and turn into a 7,8, or 10-13 inches screen as needed, rather than going for a 5-6 inch smartphone. I would rather carry a small tablet in my coat pocket.
This is why i think Apple should not follow this stupid trend of making monster sized phones, and i hope they don't give us a 5 inch 6S and 6C. At least have an option of a smaller iPhone with decent enough internals to sill do every thing fine (which actually isn't such a problem for iPhones in general, apart from Apple screwing up iOS sometimes which they can fix in an update though).
I am strongly considering an iPhone again (or a WP8.1/WP 9 if a good notification screen comes and some minor annoyances get fixed) for my next upgrade. As much as i appreciate android, i am quite tired of some of the things which is a topic for another thread, and have come to appreciate iOS again after handling my wife's new iPhone 5C. I guess i should stop here before another war starts 🙂