If you look for rule then it say F1 student are not considered as resident at any point while they are in F1 status .(When I was student I was suggested to file Resident and my friend himself filed for NR, which get got query for IRS and I did not get. and I did not get any query.. I am not telling that is right just an example )

If you are in US for more then 3 month (1xx days) per year then u need to file a resident and if live in usa for less then 3 month then u can file as a non resident. (are you aware of that rule ). I can send u the doc.