I have taken two round trips on the train which runs from Retiro station in BA to Cordoba. It is very inexpensive and the train is pleasant. There are several classes of service. I would recommend that you travel in a sleeping car ("dormitorio"), a private compartment with upper and lower berth, fresh sheets and blankets, wash basin, closet, bottled water and a packet of toilet articles. Breakfast is included in the price. Dinner is served in the dining-car. Nothing special but edible. The staff are all young and generally good natured and helpful. There is twice weekly service. I have taken the Friday departure from BA and returned on the Sunday train. Travel time is longer than the bus however the trip is in itself fun if you travel in the sleeping-car. The company's name is FERROCENTRAL. Most Argentines will tell you that the trains are very bad here and to take the bus. In general they are right however this company is the exception to the rule. The website is
http://www.ferrocentralsa.com.ar/
If you have time, also take the Tren de las Sierras which runs from another station in Cordoba to Cosquin in the hills of Cordoba. It's a recently refurbished train, a real delight, brought over from Portugal. Try to buy your tickets in advance as the little train fills up. It takes about two hours and will give you a splendid bird's eye view of the countryside. At the end of the line you can return by bus as the return train schedule may not be convenient. The bus station is across the street from the impeccable train station.
