Guerrin is probably the best place for pizza in Buenos Aires. This is a major accolade in a city where Italian food is so popular and widespread, due to the history of Italian immigration that provides the back bone for much of porteño culture.
Bife de chorizo (sirloin) is really thick, as steaks should be. There are several variants (fried eggs on top, etc.) which will be as good. Steaks are served without sauces, as they should be with top-quality meat; you can try the chimichurri sauce, made with herbs and garlic, which is on all the tables. If you like fillet steak, bife de lomo is also excellent, generously and thickly cut, but at nearly twice the price. You can't tell you went to Argentina and didn't try this!
The finest cut of beef, and likely to be the highest priced -- though ridiculously inexpensive by international standards -- is Bife de Lomo which equates to Eye Fillet. The most popular cut is Bife de Chorizo, a steak cut off the rib and somewhat similar to Sirloin or Porterhouse. T-bone steak has its equivalent in Bife de Costilla, and is generally enormous.
Puerto Madero is a great shopping and dining district in buenos aires. the outdoor mall is right on the river which is very scenic at night. Cabana las Lilas in the Puerto Madero section of Buenos Aires is often cited as the best spot for grilled beefbut you'll find a more authentic dining experience at half the cost just next door at La Caballeriza.
After BBQ and pizza, empanada is the second most popular food. There are lots of varieties, and each province has its speciality. It can be made of spicy minced beef, cheese and ham, tuna, corn, onions and other delicious combinations. A must try!