Apple removed YouTube and Google Maps from iOS 6 and that decision shows up in the chart comparing the number of unique visitors monthly for both the Facebook app and Google Maps. You can see how Google Maps fell behind Facebook at the same time the former app was removed from iOS 6.
Another chart shows that the Facebook app is more "sticky" than Google's mobile apps in the U.S. In other words, users spent more time using the social networking site's app, which actually accounted for 23% of the time U.S. mobile device users spent using apps in December. Facebook owned Instagram accounts for another 3%. Last month, U.S. app users spent 10% of their time using apps from Google. Combined, one of every 3 minutes U.S. mobile device users spent using an app in December was on an app created by Facebook or Google. The numbers that comScore used were from U.S. based iOS and Android users 18 and older, during December.
source: comScore via BGR