I'll go
The Simpsons if only because it essentially rebooted the legitimacy of the animated show as primetime programming and was a key part, along with the NFL, of legitimizing the FOX Network.
"Who Shot Mr. Burns?" is often overlooked in the 1990s MOMENTS ON TV that consumed popular culture. And it's remarkable, knowing the prior recent history of TV, that it was on an animated show on the lowest ranked and available of the networks.
I think in the end Seinfeld broke more ground. Simpsons was just a dysfunctional family. It's not like All In The Family didn't do that. But Seinfeld talked about masturbation and more down to Earth topics that eventually went on to inspire far more shows I think. For example, I see more Seinfeld in something like Sunny or Louie orArrested Development than I do The Simpsons. I think Seinfeld broke more doors down, broke far more taboos.
Check out the writing staffs for both shows though. Spike Feresten wasn't the only one to start on
The Simpsons and then move over to
Seinfeld just the only one to get a failed talk show after it.
SNL ->
The Simpsons was an infamous early conduit too.
Mitchell Hurwitz came up through
The Golden Girls so did James Vallely (the second most credited writer for the entire AD run), his first created show was
The Ellen Show. (Which also was the start for a number of other early AD writers.)
Cheers was another program that birthed the people who created the stuff we later saw as extensively innovative.
Fraiser was the dominating awards darling much like
Will and Grace, not
Seinfeld.