If you ask any local for a good parrilla (steakhouse or BBQ), Club Atenas will always come on the list, most likely as number one. The restaurant fills up quickly, so either get there early (~7:30pm) or make a reservation.
I admit that the outside is not very attractive or even resembling a restaurant, but the inside and the food will quickly put your hesitations at rest. The restaurant is on the back side of a larger sports stadium which shares the name 'Club Atenas'. Don't worry you are not going to eat in a gymnasium. The restaurant is reached by going through the parking area to the right. Again, walking through the parking area, it may give you the feel that you are going to the end of a blind alley. Continue to the last door, and just follow your nose.
The inside is decorated with white linens. There are no windows so it really does not matter where you sit. The all female waitstaff are quite busy running orders to the hungry locals. This is a local's favorite for steaks and Argentinian parrilla.
Favorite Dish: The steaks are fantastic. They are thick, juicy, tender and quite flavorful. Most will tell you to go with the File de Charizo. It is good, but you really cannot go wrong. The portions are very large, so bring an appetite.
The steaks come a la cart, so you must order your sides separately. The salads are large, possibly to be shared by two people.
The wine list is extensive but relatively cheap.
Here you can find a list with restaurants.
I´ve been & would recommend:
Cerveceria Modelo: big dishes!
Don Quijote: posh & nice meals
La trattoria: normal & sometimes bad service
la vecchia segnora: good for pasta!!
Thionis: best ice creams!!
Wilkenny: good english / irish beers! (good price as well)
We followed the advice of Lonely Planet and sought out this place to have lunch. Though it's really nothing too special, it is indeed the oldest eating establishment in the city, founded in 1894---built just 12 years after the city's founding. They have quite an extensive menu with meat, pastas, salads, pizzas, etc, all at a very reasonable price. Three of us had a full meal for 40 pesos , or about US $14.