We stayed 7 nights at Karlas apartment in heart of the Districo Federico and it was everything we could hope and more. Especially for the price.
The apartment is located on the third floor of a very secure, clean apartment building. The apartment itself was also very clean and provided all the expected and promised amenities. The location is fabulous as far as attractions (right near the metro) and has many food/shopping/bars/sightseeing within reasonable walking distance.
We were also very gracious to have Karla and Lucia (the permanent, local room mate) to help us with any advice/recommendations/etc about visiting the city. They were very hospitable and gave us a more local perspective on the city.
There is also a great roof top area of the building.
The only drawback that we faced was that the apartment was located above a small handful of late night bars, so it took us longer to fall asleep a few nights. On the other hand, there are a handful of cool, small, hip bars right beneath you. We frequented them.
Other than that, our stay with Karla was amazing.