Buenos Aires is a fantastic city with a lot of history and culture and it one of my favorite South America cities.  You get this real feel of being in Europe.  I have a great time every time I go whether it is hitting the nightclubs and bars or relaxing and eating empanelles at the outside cafes.  The food and architecture is great, make sure you check out the Obelisk (similar to the Washington Monument).  Buenos Aires claims to have the world's widest avenue so make sure you drive down 9 de Julio.  There is so much to do when visiting Buenos Aires and places to stay.  Two of my favorite hotels are the Aspen Towers and the Sheraton Towers, both places are nice and spacious.  The Sheraton is located right off the Plaza de Mayo, which is right by the river and a stretch of restaurants and bars while the Caesar Park is further into town (Centro).  Hitting the clubs in the Recoleta area is always a good time and gives you the opportunity to see some of the very very beautiful women of Argentina.  For a more relaxing time you can go to the Parque Colon and watch people.  Make sure you hit my favorite bar Maluco's for a drink