We had a wonderful stay in Oliver's apartment!
The location was perfect for us -- the apartment is very close to Plaza Serrano (but not TOO close - it wasn't too loud at night), and we were able to walk to all of the bars/restaurants/shopping in Palermo Soho and Palermo Hollywood that we wanted to. It's a very safe spot, too. It's also not far from the subway (8 blocks), so we were able to easily connect to other parts of the city.
Oliver was an absolutely fantastic host and helped us have a great stay in Buenos Aires. We would have loved to stay even longer!