I realize this question is a few months old, but I figured a reply could help anyone
Which network will perform well for you really depends on a variety of factors, including type of ad, the size of your app's traffic, and location of your users, to name a few. There are a few networks whose names come up repeatedly, as they're pretty good in most Western countries (Admob, Mopub, Chartboost, Vungle, Tapjoy, etc.), but you'll find that you will see better results with other networks in Eastern countries, for example.
The best way to monetize with ads would be to use a programmatic mediation solution, which allows you to work with several networks at once, while optimizing the performance for you. The mediation solution sets it up in a way so that all of the networks essentially have to outbid one another in order to serve their ads in your app, which means you'll make more money. A good solution will optimize for things like ad type and location, based on real-time data. Another plus would be mitigating SDK bloat from having to integrate each network's SDK individually.
You can use a mediation solution to test multiple networks on the same app, and decide which ones you like and want to keep, as well! That will answer the best/worst question for your particular app, which is a bit more useful than someone telling you what's best for
their app. Hope this helps you!
For the sake of transparency, I work for
Appodeal, which is a mediation solution