It was a better actual neighborhood before all the Arab and Russian money moved in (a generation ago, it was merely an affluent urban mixed-use neighborhood), but to me Mayfair has the ideal urban built form for a neighborhood you'd like to live in:
(apologies for the photo quality, I've seen much better but can't find them right now)
It's well-scaled, both in terms of building heights and block sizes. The architecture is nice, and also fine-grained and diverse. There are very large office buildings and also coach houses in mews. There is every form of use represented - office, hotel, retail, restaurant, residential, entertainment, even government. There's a lot of public space (two big squares, plus smaller parks and gardens). And it's quite beautiful.
There's a reason it's some of the world's most expensive real estate.