Ironically this is the first larger capacity iPhone I've purchased since I usually just get the 16gb. However, I still have my 16gb 5c as my backup phone.
64GB for both me an my wife. $100 for four times the storage is a no brainer. If it was 32GB for the upgrade I would have went with that route, 16GB just simply isn't enough these days.
32 GB is honestly enough for me and has been for the last two phones. The iPhone 6 I have on order is 64, since that's what Apple opted to make the middle level. 16 GB is too low for storing music and taking pics; if you plan on carrying movies/TV shows on your device, the 128 makes more sense.