We stayed at Martin's Alto Palermo apartment for four nights, and it was perfect. The place is bigger than the pictures show, and the apartment is in a really great location that's close to the Recoleta neighborhood (15 min walking), a bunch of restaurants in Palermo (15 min walking), and two subway stations (10 min walking) that will take you anywhere in Buenos Aires. We were greeted by Eduardo, Martin's father, who gave us a lot of really great information on the city. We walked home after dinner around midnight sometimes and felt completely safe; the extra security precautions don't hurt either! We did have some trouble figuring out how to get hot water, but a quick email exchange with Martin fixed that up quickly. Stay at one of Martin's properties if you're in BA; I know we will when we visit BA again!