As a peruvian/american I can recommend the following: Primavera Trujillana, Astrid y Gaston, Francesco, Ceviche, Mochica and Mamani (very cheap, very simple, full of peruvians). But I honestly haven't found a bad peruvian restaurant in BA yet.
3 years ago when I moved to Buenos Aires I got so sick of argentinian food, I went out and hired a peruvian cook for me and my entire office. She turned out to be incredible. 6 months ago we partnered up and recently opened Peru Deli. Our core business is delivery, we are located at Beruti 4602. We will be setting up tables in the next few weeks.
I am very happy that peruvian food is going through such a boom not just in Argentina but worldwide. Having been born with peruvian food, it is no surprise that it is among the very best. I am seriously looking at finding Thai chefs in Argentina and introduce good Thai food here as well. If you guys do come to check out Peru Deli or order, I'd love to hear your comments. We have tried to do things differently, from the decoration, to the concept, to the packaging.