It all depends of course on how you treat your phone. I've basically gone naked with mine. Just have a Caudabe Veil on there for scratch and minor bump protection and to protect the chamfered edges. It's been great so far. But then again I treat my phones well.
Yea I'm very careful but I have kids and it's hard to keep it laying around on the charger without my 2 year old thinking it's a toy , but I'm sick of not seeing the phone itself it's so nice and I wanna use it naked so screw it , I hope the silver is more durable than the black
i can only report on the (naked) iphone4, but i've dropped that one from waist height countless times on nearly every surface available with barely any visible scratches/dents (in bright sunlight you can see a few, but that's it). once it even slid on gravel path for about 3 meters (got some nice, but still barely visible, parallel scratches from this).
as the 5 and 5s got newer gorilla glass and an aluminium back, i'd guess they are even tougher.
i've seen a few broken screens as well on other peoples phones who seemed to need just one unlucky drop for this - but i guess you'd need a pretty tough case/protector to avoid that one pointy stone that's destined to be your phone's doom.
i'm usually not really careful with my devices, but i'm also not exceptionally careless - the only apple product i ever managed to destroy was an ipod classic 20g, i accidentially jumped on. and even that one lived for another three days (btw. ipad: 1, ikea aluminium trashcan: 0 )
i have a white/silver 5s, no screen protector or no case. just have a tiny tiny tiny chip type mark on top bezel, only see it if sun hits it the right way. i usually keep phone by itself but theres been a few times ive had it in my jacket pocket with keys on accident. holds up so much better then the black one
i had it in an incase slider case that had two parts, what happened was that something got under the case, and once i slid it off it dragged it across the phone scratching it. they fixed this with their newer one by putting a cloth back to it and sliding not against the phone, i had that case for a bit but then got the apple case and couldn't go back.
My naked 5 is looking a tad used now (not bad for nearly two years running though, a little paint rubbing on the chamfer) then again my ex naked 5S work phone is looking worse after dropping it at work. Massive chassis dent (screen is fine but I can actually see into the phone slightly, cased it now!)
Stick it in my pocket with keys, small work tools, loose coins etc. I abuse the things. Still never broken one though.