I only ever use screen protectors and never cracked my screen in 3 years with iPhone 4 and 5s. My sister uses otter boxes and she cracked her screen...twice.
Same - I've had my iPhone 4 for 4 years, without a case and just a front and back screen protector (because the front and back are both glass on the iphone 4) and it hasn't got a single scratch or crack in it... some girls in my grade will get a new phone, like the iphone 6 and crack it the next day -_-
..I'm poor as hell