You would think that the most popular Android app would be one of Google’s own, but a recent report from Nielsen shows that Facebook was the most used app in the U.S. during the last 30 days. Facebook was found to be the most active app among users 18-24 and 25-34, where it rack up an amazing 80% usage.

When it comes to app stores, Google’s Android Market topped the charts with usage rates of 89-95%. This should come as no surprise since it comes pre-installed on most Android devices. Amazon’s Appstore, which debuted this year and must be manually installed, made a strong showing with usage rates of 14-24%.

The most popular game was Angry Birds, which ranked highest among the older age group. Usage rates by age were 22% for 18-24, 29% for 25-34, and 35% for 35-44. Zynga’s Words With Friends also ranked highly with usage rates of 21-25%.

Check out the chart below for the full break down. Which results are most surprising to you?