The letter classification is used for market research and segmenting the population based on purchasing power. They also use it in the television industry, print media and such. AB are generally the better areas. Off the top of my head they would be Piantini, Paraiso, Naco, La Esperilla, La Julia, Bella Vista, Mirador Norte, Mirador Sur, Los Cacicazgos, Los Restauradores, Viejo Arroyo Hondo, Cuesta Hermosa, Cuesta Brava, Altos de Arroyo Hondo, Altos de Arroyo Hondo II, Altos de Arroyo Hondo III, Arroyo Manzano, Puerta de Hierro, Urb. Fern?ndez, Las Praderas. All within the National District. There are many more, but can't remember which ones.
In Santo Domingo Oeste there's Villa Naco and a few others.
In Santiago La Trinitaria, La Esmeralda, Cerros de Gurabo, Quintas de Pontezuela, and many others.