Flip a coin.
Honestly, I'd pick the 5C. It'd feel better in the hand and it's universal device with just about every single LTE band you can get these days.
Although for $150 more than the 5, I'd probably just pick the 5S. It will last longer and get you better resale value if you go to offload it in a couple of years.
But, at that point, you should probably consider other carriers, like TMobile's $30/mo 100m 5GB data plan or AT&T's Aio Wireless, unlimited talk, text and 2GB of highspeed data for $55.
Switching to a GSM carrier will also give you way more flexibility in your devices, at least for the next couple of years.