If you ask 5 different Argentines this you'll get 5 different answers, so there isn't really a best, however my favorite is Don Julio in Palermo. La Hormiga is high quality too. If you want the best value for the money, go to Estilo Campo in Puerto Madero, still world class quality but often half the price as the more famous ones. Many though are just overpriced tourist traps, stay away from ones like Cabana Las Lilas. I've found you can judge general overall quality by testing their chimichuri, so I normally ask to try it first to see if it's up to code when trying a new place. Bad chimichuri will normally mean poorly prepared meat, if they can get a complicated sauce like chimichuri right though it means they're educated meat men. When purchasing more exotic beefs like Kobe I would also recommend to ask to see the raw meat first to verify authenticity and ask about it's source, I've seen them passing off normal meat as Kobe before.
Outside of the meat the food in Argentina is horrible though.
Yes, of course. When I'm going to a place that's "fine dining" or "exclusive" I don't want to have to deal with low quality, 3rd world bullshit. Especially when entertaining, if we're seated by a grumpy 60 year old male, then shown a few pieces of hard, store bought bread with garbage "french bread" that's bought from the panaderia around the corner, with half ass criollo & vinegary chimichuri sauce, we'll smile, shake our heads no and leave. That's exactly what's happened at Cabanas Las Lilas (except add in tables full of screaming, smoking Asians, not the type of experience I'm after personally but to each their own).What? You go to a restaurant and ask to try their chimichurri before making your order? At what point do you do this? Once you've been seated? As soon as you walk through the door at the counter? What if its not to your liking? You just leave? Sounds like you're a bundle of fun to eat out with. Odd.