Native push, as they are called, are the hottest trend right now. Users can receive notifications even when they're not viewing a Publisher's website, so long as the permission to display the notifications is active. This ad format is highly compatible with all types of offers due to its customizability.
The pop-under format opens a window behind the content of the user’s active window, containing the advertiser’s landing page. This ad format is mostly used by Single Opt-In offers.