Why was katy perry last friday night chose first and party rock anthem was 2nd?

I don't see the reason party rock anthem by LMFAO was second. I mean
it's better than katy perry last friday night so why was it chosen
second in americas top ten songs or something I really dunno what it
is called. ohh and please answer which one u think is better party
rock anthem or last friday night by katy perry?