I've never used a screen protector on any of my iPhones (original, 3GS, 4S, 5S, now 6). I did get a decent scratch on my 3GS but I think it was from someone dragging it facedown across a surface that had some sand particles or something on it, or possibly a cat claw jumping off of it on my nightstand at some point? My 5S had one minor minor surface abrasion that I couldn't see at all unless i got it to one specific angle in perfect lighting conditions with the screen off. I'm not sure where that scratch came from but I suspect it might've come out of the box with it and I never noticed. Screen protectors really aren't necessary unless you keep your phone in the same pocket as your keys or you're so anal that a microscratch you can't even see will drive you nuts. Personally I'll take 1 or 2 years of using my phone without a buffer between me and the screen over unncessary protection as long as you are careful.
