I actually did study there for 2 months and really improved my Spanish. We focused on all areas of reading, writing, and of course conversational Spanish. I was really impressed by the quality of the teachers. Plus with smaller classes, I felt that I was able to really focus on improving my Spanish. Of course I still need more practice!! Downers - have to pay for the coffee and sometimes have to take the stairs, as the elevator sometimes doesn´t want to work. Overall, very pleased.
Haven´t studied in other parts of Argentina, but think it would be best to be in BA, as it will give you more time to explore the city.