Buenos Aires [1] deserves all the time you can give it. Those planning an extended stay, say two weeks or more, should acquire Moon Buenos Aires [2], which has exhaustive coverage of the capital and more detail on excursions in Buenos Aires Province and neighboring Uruguay.
At a minimum, though, figure three days for highlights like the Plaza de Mayo [3], adjacent sights like the presidential palace [4] and cathedral [5], and the Avenida de Mayo and Café Tortoni [6]; the southern barrios of San Telmo [7] (preferably on a Sunday) and La Boca [8]; and the Teatro Colón [9], Recoleta [10] and its famous cemetery [11], and Palermo [12] (including the MALBA [13] art museum).
But that’s pressing it, and at least a week would be desirable for seeing those sights thoroughly, at a more leisurely pace, and taking in the Puerto Madero [14] waterfront, Palermo [12]’s parks and fine arts museums, Chacarita cemetery [15], and the Paraná Delta [16].
Even that would permit only limited partaking of the rapidly evolving restaurant scene in Palermo Soho, Palermo Hollywood, and Las Cañitas; the vibrant cultural life (including art galleries and theater); the hyperactive nightlife; and even compulsive shopping at Galerías Pacífico [17] and other recycled landmarks.
No matter how much time you spend here, there’s always more to see and do.
Links:
[1] http://www.moon.com/destinations/argentina/buenos-aires
[2] http://www.moon.com/books/moon-handbooks/moon-buenos-aires-third-edition
[3] http://www.moon.com/destinations/argentina/buenos-aires/sights/monserrat/plaza-de-mayo
[4] http://www.moon.com/destinations/argentina/buenos-aires/sights/monserrat/casa-rosada
[5] http://www.moon.com/destinations/argentina/buenos-aires/sights/monserrat/catedral-metropolitana
[6] http://www.moon.com/destinations/argentina/buenos-aires/sights/monserrat/cafe-tortoni
[7] http://www.moon.com/destinations/argentina/buenos-aires/sights/san-telmo
[8] http://www.moon.com/destinations/argentina/buenos-aires/sights/la-boca
[9] http://www.moon.com/destinations/argentina/buenos-aires/sights/microcentro/teatro-colon
[10] http://www.moon.com/destinations/argentina/buenos-aires/sights/recoleta-and-barrio-norte
[11] http://www.moon.com/destinations/argentina/buenos-aires/sights/recoleta-and-barrio-norte/cementerio-de-la-recoleta
[12] http://www.moon.com/destinations/argentina/buenos-aires/sights/palermo
[13] http://www.moon.com/destinations/argentina/buenos-aires/sights/palermo/malba
[14] http://www.moon.com/destinations/argentina/buenos-aires/sights/puerto-madero
[15] http://www.moon.com/destinations/argentina/buenos-aires/sights/outer-barrios/cementerio-de-la-chacarita
[16] http://www.moon.com/destinations/argentina/buenos-aires/vicinity-buenos-aires/the-delta
[17] http://www.moon.com/destinations/argentina/buenos-aires/sights/microcentro/galerias-pacifico