I was in Buenos Aires 3 years ago for a few months, and was taken to 'Siga la Vaca' by my local host. The name means 'Follow the Cow' and it is a large, buffet-style, restaurant that is super-popular with the locals. There was a 30 minute waiting list when we showed up. It's right on the river in an awesome location as well.
The meat station was fantastic, where they cook everything over flame.
I wish Melbourne had a restaurant that cooked meat even 1/2 as good as they do in Buenos Aires. They seem to have mastered the art of it - which involves cooking over smoky wood fire, in some cases for hours.
In fact, I never went to a bad restaurant the whole time I was there. The touristy strip in Recoleta had quite a few excellent restaurants as well, and they're probably considered the 'worst' and most-expensive by the locals.