Steaks and beef products are beyond excellent in Buenos Aires. Once you get to Patagonia, lamb is incredible. If you are a little adventurous, I would try more than just steaks. Kidneys, sweetbreads, blood sausage, chorizos, bull balls, intestines are all yummy.
You will get a lot of advice on high end steak places. My 2 favorite places are La Estancia (LaValle 941 in the downtown area) and across from that is El Palacio de las Papas Fritas. The latter has great meat, steaks and other dishes and the most amazing fried potatoes called papas souflee which are puffed fried potatoes.
Both places are very reasonably priced, they are in the "tourist area" but they have been there for at least 40 years and still going strong.
By the way, make sure you order Charlotte almendrado for dessert. An iced desert cake with crunchy almonds and chocolate.