Definitely not 4S. I work for AT&T, and I see a lot of people complaining about how slow the 4S is now with iOS 7 running on it. Also, the 4S only comes in 8gb now for free. Just go with the 5C. It's a great phone, and like gcom said, the difference between that and the 5S isn't super noticeable. The 5S has a better camera, a much faster processor, and Touch ID.