AdAway for rooted devices allows you to modify you hosts file directly. This means that AdAway doesn't have to be constantly running in the background to block ads. It modifies the file then closes.
I usually use AdAway with root and with my pihole at home (and outside home with VPN) and I barely see any ads, although I haven't tested with Android apps.
Its basically just a host file. It pulls in a huge file with all the ad domains and whenever your phone tries to connect to one it gets ignored. Therefore it also works for ads in apps.