earlyretirement said:Palermo and Recoleta are by far the nicest, most upscale and central neighborhoods of Buenos Aires.
I wouldn't have any desire to live in any other areas besides either of those two areas. Not to say there aren't safe and nice areas like Barrio Norte or Puerto Madero but for nice areas and being Central and availability for pretty much everything you need, IMHO nothing beats Recoleta or Palermo.
There are some REALLY nice areas of Belgrano also, but has less nightlife and other things that might be more interesting to expats and visitors than Palermo and Recoleta.