Manchester City are more interested in Champions League but they don't sacrifice Premier League. If they can not win Premier League, it can be because another competitor have too good performance in this season to beat Manchester City.
Usually even if Manchester City lose concentration for Premier League, they are still too strong there and can win it. It's kind of an easy task for Manchester City and they can have very big difference with latest club on the table. However, in this season, if they are not careful, Arsenal will take the trophy from them.
The Champions league is the toughest league to win, to win the Champions is hard to predict. I think Manchester city puts Premier league first because they are used to the game in Premier league. Last season Manchester City were thinking they would win the Champions League but they missed it at last.