There is a great Argentinian style steakhouse in the hotel zone in Polanco, right near the Nikko, Intercontinental and Marriot on Temistocles. Its called Gaucho Grill.
It would probably be wise to avoid going Sundays lunch time because it gets very crowded then

Another good option for steak in MEX is the Rincon Argentino chain of restaurants.

In my opinion the best Steak House far and above any others is Rincón Argentina. There are a few around the city, however, I have been told the one in Polanco on Presidente Mararyk gets the best cuts of the lot. Definiately not cheap, but if you have ever eaten beef in Mexico, you won't mind paying the price for excellent beef. Also, Cambalche has good beef, but again the one in Polanco seems to have better beef than the outlying ones.