My husband and I were in Buenos Aires this past week and I wanted to share with you some of the great restaurants we visited. I found this site incredibly helpful planning the trip and wanted to pay back the favor. We stayed at the Four Seasons, however I highly recommend La Faena. It is a hotel and also has a fantastic restaurant. The steak tartar, duck crepes and empanadas are incredible. The atmosphere both inside and outside is perfection and great for a relaxing afternoon. Tegui was the best meal of the trip. We opted for the 8 course experience to taste more of the menu and it was incredible. If you are going to order off the menu, I highly recommend the brussel sprout ravioli. They were amazing. La Bragada was a perfect neighborhood restaurant for incredible meat at great value. L'Oviedo was the only let down. Our service was horrendous and half our party speaks spanish so there was no language barrier. I thought the paella was good, but several in the group were not satisfied. The dessert however was amazing. Overall though just a mediocre experience.
Hope that helps. Have a great time, but if you're traveling to South America - I would recommend Santiago over Buenos Aires, hands down.