I want to create my own in-app ad mediation, and want to know which have the best eCPM (with a good fill-rate) ad-networks for an iOS casual game in the following GEOs:

1. Brazil, Mexico, Colombia (LatAm countries)

2. USA, UK, Germany, Australia (Tier 1 countries)

Thank you for the help!

Sometimes you can be limited (not impossible, but there may not be plug-and-play support) by the game engine you use.

Could you expand on this?

Well, it's a native iOS puzzle game written in Cocos-2d. It should support all major ad network SDKs