Selena Gomez song - Rock God .
she did really good!! i like katys a TINY bit better cuz katy can really hit those high notes but i still LOVE selenas .
And yes! Katy Perry wrote this song & sung it and all, but SHE gave it to Selena, big deal. I think Selena did great with this song! Katy & her should totally sing this song 2gther live one day .