When you come to Buenos Aires, or even just travel in general, I highly recommend staying in a hostel. I came to Buenos Aires completely alone, not knowing anyone, and have met some of the best people at the hostel at which I am living. I bonded with my roommates almost instantly and they eagerly accepted me into their bigger social circle, and in addition to making long term friends, I have met some of the nicest, coolest people just passing through: Peace Corps volunteers, international med school students, back packers from America, the United Kingdom, and France, and Argentina locals just visiting the city.
Hostels are filled with interesting, kind people who eager to talk and spend time with you, and I truly believe they are some of the best places to meet people while you are travelling. I made my entire social circle in Buenos Aires through my hostel and I could not be happier. Even the people I met and only knew for a few days changed my experience abroad for the better. I would not rather stay anywhere else.