Buenos aires best steak house
Here's a take from an ex-New Yorker foodie now living in bsas.
The "best" depends on your tastes and mood. These 3 all use the same supplier, who's considered the best source in the country:
The meat at Cabrera is always superb. Cabrera offers the widest variety of cuts in the most generous portions, almost always grilled to the proper temperature, and prices are quite reasonable. That said, they accept reservations only for the first seating (8:30 PM), and there's a long wait on the sidewalk after that (with complimentary champán nacional to sip while you wait). Since most porteños refuse to reserve or to wait, the place is usually jammed at prime hours with Yanquis and Brasileros cranky from waiting. By 1100 on weeknights, you can usually walk in and get great service. I prefer the Cabrera Norte, a half-block up the street from the original corner location, where there's a little more space and a good deal less noise.
Le Grill in Puerto Madero, already mentioned, is quiet, elegant, and well-served, with a good bartender (totally lacking in Cabrera) and a direct view of Calatrava's Puente Mujer. Portions are moderate and prices are high (for Buenos Aires).
Elena, in the Four Seasons Hotel, is also somewhat pricey, and the portions are more like 12-once instead of the sharable platters that arrive at Cabrera. The atmosphere is a little more lively than Le Grill and the service a little less formal. The menu is only half steakhouse fare, and the rest of the offerings are just as terrific. The menu lists beef in 3 categories: traditional Angus, dry-aged (new to Argentina), and argie Kobe.
For buffet style, I assume you mean "tenedor libres" or all-you-can-eat restos. None that I've tried have meat at the level of the 3 listings above, but the Rodizio on the costanera past the local airport (and not the branch in Puerto Madero) serves high-quality meat in good cuts. It also has the best salad bar in the city.
As for a cheap one, by US dollar standards any of these will qualify, including Le Grill. In fact, I haven't been to a cheap parrilla in years because even the best grill restos here are affordable.
Regarding earlier recommendations, I'm also a fan of La Brigada in San Telmo. The beef may not consistently be at the very top level, but it's always good, and the place is relatively comfortable. I am not a fan of the Cabaña las Lilas, where I've never been served anything better than so-so beef, at relatively high prices, surrounded by tourists congratulating themselves for being there.
Other spots you might enjoy are Fervor, behind the Alvear Palace hotel, to hang out with the Recoleta gentry. Along the costanera, Happening and, especially, Gardiner are deservedly popular with locals. Miranda in Palermo Hollywood can also be fun, with good beef and an updated take on the traditional parrilla (rock music, tattooed waiters in tee shirts, young crowd).
Hope that helps!
I, too, liked Cabana Las Lilas very much even though many people will tell you it is a tourist trap. I did not find that to be the case and enjoyed my meal very much. I would suggest the Ojo de Bife (ribeye) cut which was quite flavorful and pass on the couvert plate that they bring out in the beginning--it appears to be complimentary, but you will be charged for it if you eat it. Same owners of Rubayait in Sao Paolo....I also enjoyed La Cabrera.
The "best one?" Hard to say, but overall, my beef eating here (maybe 3x/year) hasn't been that satisfactory over the past couple of years. I was quite pleased last night with Le Grill in Puerto Madero. Very nice ambiance, prices were fair, and service was very good. Meat was the best we've had in ages. They are currently offering 20% discount on food (not beverages or service) for certain days/hours when you make a res on Restorando, and pay w/cash.
Buffet? La Bistecca remains popular. Meat ranges from meh, to not bad.
Cheap? Probably no longer worth the bother, as they aren't really cheap, i.e., DesNivel now wants $120 for a lomo a la mostaza, and the plain lomo is $85.
Given the quantity of feedlot beef polluting the country, cheap only leads to disappointment, and even at the higher prices, you will have quite varied experiences.