Huh? OP has a 16GB sprint iphone 5. Thats basically the lowest priced iphone 5 out of all providers. Brand new S4 for $400 is a very good deal considering that they are selling in 500 range currently. S4 right now is worth more than 16GB iphone model. Its worth more than att and verizon 16GB models. Once 5s comes out then 5s will be worth more and 5 will drop further in price than it is now.
The iphone 5 is still worth more. Well maybe cause he has Sprint it is worth less. I just sold a black verizon iphone 5, jailbroken with ios 6 on it. Perfect condition, like new. And it went for upwards of about $500 on ebay. With the case and accessories. So yes they do keep their value. If you look at listings for newer phones like the htc one and s4, it is hard to find one going for a good chunk, unless it is practically like new in box. And my point is, if i for example had an s4 compared to an iphone, that a few months down the road. It would depreciate alot faster than if i had an iphone 5. Which holds it value longer.