Should I get a 16GB,32GB or 64GB iPhone 5? - It depends on how many photos, apps, songs, movies, games, etc you plan to have on your iPhone. If you have lots & lots of "stuff", then you'll want to get the larger memory phone. If you keep most of your stuff on your laptop, & just take a few things on your phone, then a smaller memory phone would work great. The main thing is to remember that you never want to completely fill up your phone. I personally think the phones work better when you have several GB free. That has been my experience. One thing to consider, however, is not just what you have now, but what the App Store will have in the future. Newer apps, games, etc., may be larger & more memory intensive. It be a bummer to buy a phone & realize 6 months later that something new & incredible has just been released in the app world & you don't have enough memory to accommodate it. Think future.
Safe bet is a 32 GB, it's enough for most apps, photos and videos. I use iTunes Match, which means you don't have your entire music library on your iPhone, which takes up most of the space. If you do not want to use iTunes Match (for example because you want to be able to play your music in the woods or on an airplane), go with the 64 model. I personally think 16 is too meagre for any intense use case.
