I've eaten at El Mundo a few times, as they're around the corner from my apartment. Pretty good, but not in the top 20% of my favorites.

I ate at El Yugo this week, and got an Ojo de Bife. Decent, but not too flavorful. Service was good, as I was the only one in the restaurant for the first 30 minutes (I arrived at 8:15pm). I also got the Flan Mixta which was very good for 9 pesos.

I've still gotten some of my best meals at L'Alliance on 945 Cordoba near Suipacha. Don't make the mistake of going into the bigger La Chacra restaurant (with the cow out front). They have a very nice grill going. Prices have gone up a lot for beef over the last two months, but still very reasonable for the quality you get. I got an excellent Bife de Chorizo two months ago, for 23 pesos, it's now 32 pesos. It's run by a US Expat, and he has some very nice menu items. Even the small pizzas for 10-12 pesos are a great deal. The chicken pesto is easily a full meal in itself, and the empanadas are the best I've had in Buenos Aires.