Depends on whether you want "new" italian, or classic Argentine/Italian.
To me, the real Buenos Aires is not just about food, its about atmosphere and history- you can eat at fancy noveau cusine places with modern interiors in any city on earth- but the funky authenticity of some of the classic Buenos Aires restaurants is unique.
I like Pierino-
http://www.guiaoleo.com.ar/detail.php?ID=377
Its been in business, continuously, with the same family running it, since Astor Piazzola used to hang out there.
Its homey and not pretentious, and you basically order whatever the grandmother is making fresh that night.
Really good fresh pasta.
But its not in Recoleta, although its not too far.
For steak, La Cabrera is still a good place to take first timers- huge steaks, korean style (in concept, not in taste) array of small plates of side dishes included, and while parrilla fans will quibble for hours about how its not as good as it used to be, it seldom disappoints visitors from out of town.
Or, for a very Porteno time machine kind of meal, I love 1880, on Defensa in San Telmo across from the park.
You could be in 1930, or 1950, or 2010. The waiters will treat you right, the food is good, and when you are done, you will not think you have eaten in Paris or Tokyo or NYC- its very Buenos Aires.
http://www.guiaoleo.com.ar/detail.php?ID=1059