There's no comparison actually . Ronney after all is a center forward, but he is capable of playing as attacking midfielder, that's the main difference. With Rooney they can have 2 goalscorers in the game and creativity but with Kagawa less goalscoring, and that happens because Rooney is who he is. Personally im always of the opinion that Rooney has to play as center forward, he may work as playing a little bit more deep and free but playing him so deep and even sometimes as central midfielder is just wrong..