We enjoyed Mariana's apartment. The view is truly spectacular, probably the best in Buenos Aires. The location is perfect with quick access to everything you need. The apartment was clean when we received it and Mariana was quick to respond to our need for a second pair of keys.
I have read a few reviews about the elevator noise in the bedroom. Yes we heard it but it did not affect us much. A bigger and more comfortable bed would have been a plus. If there are 2 sharing the bed and one of you is 6 feet, 200 pounds it will be tough if your stay is more than a week.
We had a great time in BA and we would recommend Mariana's apartment.