Has anyone used advertising agencies like admob, AdSense etc in their websites or apps and anyone have great success stories to share with them? I get it "depends on the app or website" but I wanna know if anyone has managed to get a decent amount of monthly earnings from it.

Nope. don't even try.
it goes like this: their algorithems favor very small (100 hits/month), or very large (1m hits/month). Anything in the middle - will provably get you blacklisted forever.
Reason: they use a simple anomaly detection std dev bands approach. if you have too many "spikes" in the visitor pattern - they will blacklist, with no appeal, or a human to talk to. when you have small amount of visitors per month, the stddev algorithem is disabled, and when you have 1m per month, 2k spikes are acceptable. But when on day 1 you have 1k visits, day 2 3k visits, day 3 .5k - it is "you cheated us, bye bye".

You can avoid by managing it carefully though - not worth the effort though.

@magicMirror woah thanks for the info that does align with my experience so far too

My company does a lot of media consultancy and media science. Google Analytics, Google Campaign Manager and Google Display and Video 360 seem to been the way to go