*discussions.nokia.com/t5/Nokia-Lumia/Re-lumia-520-broken-screen/td-p/1906656
That lumia 520 was in a protective case and stilll broke..
it actually depends on the angle at which it is dropped.. No matter whether the phone is made of chimpanzee/gorilla/monkey glass and no matter what the brand is if it drops at a wrong angle even a slight drop from knee height will break it..
i have an old HTC explorer and it must have dropped around 40-50 times in 2 years from 4 feets i am very careless
, and i have also seen the same phone's screen got broken by just a slight drop
What you should check is that the build Quality of plastic is good or not .. lumia 520 is already very strong like all nokia phones are ,, gsmarena mentions strong build quality of E1. but go out and check both of them at a store and see what suits you..