Ad Exchange is known to have the best fill rate among all ad networks. However, in the bidding process, Ad Exchange may sometimes be unable to win the battle, meaning you’ll need a backup for an ad impression to target. This strategy allows publishers to monetize every single ad impression possible without having to worry about gaps.
Some of the ad networks known to fill at 100% across all geo-targets are:
We recommend using CoffeeCup FTP to set up a passback URL. Its interface is fairly easy to navigate — you can check out How to Create Passback URLs With CoffeeCup: 10 Simple Steps for a quick guide.