Something else to consider is that you can move your existing iPhone 5 to tmobile and experience some minor network issues (you might not get LTE). You can't use your iPhone on Sprint at all. If I were you, I'd move your i5 to tmobile and then trade it for a 5S when it comes out.
As everyone else said above, Sprint is pure trash. More promises and promises of network upgrades and never any action. How did they start rolling out LTE last year and T-Mobile is already on pace to catch up with an surpass them in LTE coverage this year? Or how AT&T/Verizon have more LTE than Sprint has 3G? Or worst of all, Sprint 3G speeds actually GOT SLOWER this year compared to last year. Totally inexcusable. Average speeds for Sprint "3G" are comparable to AT&T or T-Mobile EDGE data speeds.
Honestly anyone getting an iPhone 5 on Sprint is wasting their money. Why buy a premium device and cripple it with a network made for dumbphones? Unless you happen to live right near one of their small areas of LTE or spend most of your time at home on Wifi, they are almost useless.
I don't have much high praise for T-Mobile either because of their lack of high speed data outside of cities but at least they have pretty solid data speeds in most major cities. Sprint is just garbage all around. I don't even know how they're 3rd.