The top mobile application in the United States during 2012 was Facebook, according to a net metric published by comScore. The social network surpassed Google Maps right around mid-September when Apple decided to ditch the map platform for its own solution. Google Maps continued to fall, in terms of overall unique impressions by U.S. users, until about mid-October when its ascent started again. The two applications are set to continue battling throughout 2013.

“Google Maps has been clawing its way back the past few months after getting reinstated on iOS 6, so look for the competition for the #1 spot to heat up as we head into 2013,” comScore said. Facebook notched in a unique visitors score of 85M in December, followed by Google Maps with 74M, Google Play at 61M, Google Search at 60M and Gmail at 53M.

“In addition to owning the top app audience ranking, Facebook has consistently ranked #1 in terms of mobile app engagement,” comScore explained. “Their app currently accounts for 23% of time spent on apps, while sister app Instagram owns another 3% of the market. Various Google apps combine to account for 10% of time spent, with Gmail owning the highest individual share at 3%. These two leading web companies combine for more than 1 out of every 3 minutes spent on mobile apps.”

Google dominates the top 5, so it could be hard for another social network or application to break through into the top rankings, but Pandora isn’t too far behind, and who knows what kind of other new apps we’ll see this year?