I think in Britain, the greatest sitcom has to be Only Fools and Horses.
It was relentlessly funny, and charming for 11 years.
All the characters were diamonds.
So many of its catch-phrases passed into everyday use in British English. Most noticeably Luvly Jubbly and You plonker, Rodney.
There were jokes that you could see for years without ever noticing them that suddenly became clear; like the fact that Trotter's Independent Trading, which was written on the van ended up as TITCO
It didn't start to get bad after so many series, and as Del-Boy would have said, it's finishing story was a belter, which rounded off the tale of the Trotters perfectly.