GameStop is more convenient. No fuss no muss. Cash. No weirdos.
AT&T 32GB 5S trade in is $243 cash at GS (current online quote) vs. $316 at Amazon (good condition). $304 store credit at GS isn't bad if you buy stuff at Gamestop. In my case I spend plenty at Amazon and can't remember the last time I set foot inside a GameStop. Whatever works for ya.
If you are not a teenage girl I question the reason for a case.
Don't be so myopic and judgmental about why people use cases. It makes you appear to have the same emotional maturity as those teenage girls.
I use a case on my phone because I choose to do so. What other people do has zero bearing on my decision. I've tried iphones naked and prefer using a case. For me: It gives a bit more grippiness lessening the chances of a drop and a little bit of protection if I do drop it. It also eliminates me worrying about whether the surface I set my phone on is gritty or rough. Not because I'm really that concerned about resale but because I hate messing up my stuff. I used an Apple leather case for my 5S and really have enjoyed it. I also used an Incipio Feather on my 4 and 4S.
(I'm NOT trying to do a case vs no case debate; I honestly don't give a hoot what you or anyone else chooses to do...)