Fawlty Towers might be my all time fave Britcom, due to Cleese, and the writing. Every episode was brilliantly written.
Equally my fave would be Are You Being Served. There is no way, on 1973 American TV, that a character like Mrs. Slocombe could say, (regarding the trophies on her mantle), "There for my pussy, it gets an award every time I show it".