What are the best mobile ad networks to promote your app on android?

I recommend Affle - Mobile Audience as a Service Platform, a programmatic attribution analytic led mobile marketing platform which has been running one of the best campaigns.
One of the best ad networks when it comes to reach, traffic quality, pricing and ease of use is - Affle's Ripple Ad network. Ripple helps you reach the right audience at the right time in the right way. When it comes to reach, its among the top players in terms of number of impressions per day. In terms of quality traffic, its data centric approach for ad inventory accumulation lets you target the right traffic.