I was thinking more format-wise than longevity considerations, though appreciate we're getting into the realms of this thread being personal favourites vs. what would actually be considered the "landmark" sitcoms, so to speak (Darkplace falls more into parody than sitcom for me, hence I wouldn't have otherwise mentioned it. I think for example, if you could have Darkplace as a sitcom, you could have Look Around You as well).
Being as objectionable as possible, one reasonably couldn't have a conversation about "best" sitcom without Friends being in the mix, for example, yet I don't think there's been a mention of it in the thread thus far I believe?* It walked on the heels of Seinfeld, it's aged very poorly in places, but if we're talking cultural impact, popularity and longevity, it has to be up there.
Nathan Barley was tremendous.
*@Genie got it on page 1.