It just struck me recently and I'm sharing.
As a millennial who enjoyed these shows as a young(er) adult ... I cherished them both, and at the time probably like 30 Rock more, and probably would have said that it's "the better comedy".
Over time though I've noticed I basically don't really think about 30 Rock ... frankly I almost certainly think about Seinfeld more ... but Community has "seeped in" to my TV subconscious fabric.
If I were to re-watch either right now, it'd be Community hands down. It'd be heart warming and comfortable and, I suspect, more relevant or still meaningful. By comparison, I wouldn't be surprised if 30 Rock would feel more dated, "noisy", and kinda culturally narrow and specific in a not-coincidentally SNL-like way.
30 Rock may still be "the better" TV Comedy (whatever that means). But it was written by a TV writer about making TV in New York, while Community was written about TV and its fans, IE "us", living in any random city.
I loved community... Until the second episode of paintball and then it started to feel generally recycled. But man the first couple seasons are good. Have not tried 30 rock.