There can be only one. Since The Simpsons created the modern adult animation boom (we didn't forget about you, Fred Flintstone), there's always been a show that captures its zeitgeist. I'm not talking about personal preference here; I'm talking about the show that was undeniably the most popular entry in the adult animation genre.
The Simpsons served as the sovereign for a while. South Park claimed the throne in the late 90s. Family Guy reigned supreme in the mid-00s. Nowadays, Bob's Burgers has become a front-runner in adult animation, but Rick and Morty seemed primed to lead adult animation into a new golden age. In the video embedded above, the YouTube channel Toon Fridge talks about how Rick and Morty instead became the recognized face of cringe culture on the internet.