One of the best places I've stayed in so far in Buenos Aires (out of around 10 different places).
First of all, I work online, so the most important is internet. The internet works great.
Second most important cause I'm a Canadian is quiet. A very quiet apartment. I slept well.
Now for the rest. The location is great. Just two block from Santa Fe and a few blocks from Palermo. A big grocery store is just a few meters from the entrance. If you like to work out, a gym is located beside the entrance. Another gym with swimming pool is located one block away.
The apartment is on the 13th floor. Maybe the only thing that was annoying was how long it took to get all the way up the 13th floor. If you like being high up, then not an issue.
The apartment is not facing the street, so it is quiet. Blackout persianas keep out the light for a good night's sleep. The bed was comfortable.
The kitchen is more or less fully-stocked. It doesn't have the nicest kitchenware, but it will do for the basics.
In the mornings, you get sunshine coming in through the window and hitting the couch in the living room. A great way to get some rays. There's a TV with basic cable if you want to catch up on what is happening in the country.
The neighbors are quiet. The only time I had problems with them was when the one neighbor left their dog home alone a few times. It would bark for hours. Normally in Canada we would put the dog in the bathroom with food and water as to not bother the neighbors/lessen the noise, but it seems like something they don't do here.
Buenos Aires is a pretty safe place, but if you're really worried about security, there is somebody at the entrance 24/7.
As for Mariano, a great host. He checked up on me weekly and was always ready to help.
I give this place my recommendation. Everything is great. Only cons are the neighbor's dog when home alone, basic kitchenware, and not the most comfortable chairs to work in if you work from home. At the same time, you get great bang for your buck.