Rooms are small.... staff is quite umpolite... and to end up, the area has not so many attractions as you may want see.... apart from Plaza de Mayo and government house... nothing more than that..
Try Palermo Soho!!! trendy hotels, nice people, great restaurants...
Check Soho all suites or bobo hotel!

NH City Hotel is very well located, near from Plaza de Mayo and Casa Rosada, in downtown of Buenos Aires. So, you have a lot of options for transportation (taxis, subway, buses).

The room is very nice and clean. I stayed in a large room, with a living room and a bedroom, closet and the bathroom. The furniture are not modern, but are comfortable.

The staff is very polite. Services are very good (the restaurant is good). For the price (about US$ 90 per night), it is a very good choice.

Stayed for three nights on a business trip. Location is perfect, but that's all regarding positive feedback. Unprofessional staff incredibly slow both at check-in and out, smallish and outworn rooms, elevators stopping half-way without any reasons (happened at least three times), a gym consisting of two bikes and two treadmills, both old, dirty and outworn, no towels available. Took us several attempts and several calls to book a meeting room what should be done within two minutes. Internet access at business center not working. On the bottom line: Not recommended - seems that this hotel has seen much better times....

Stayed here for 8 nights in March, attracted by the central location, rooftop pool and attractive deal on Hotels.
The hotel is a lovely 1930s Art Deco bulding which has been been given a complete makeover. The lobby and restaurant are spacious, stylish and modern in appearance. The pool is very small but the surrounding deck is a pleasant place to soak up some sun and commands an interesting view of the downtown area. The youthful and enthusiastic staff did everything we asked for with a smile.
The only downsides were that our room, while comfortable, was rather small. Also the area is full of banks and government departments and dies at nightime so you need to travel a bit to find most of the restaurants and bars.
I think this hotel would be very good for someone on business or loves the sun. If you don't fall into these categories then perhaps somewhere in Palermo, home to most of the best restaurants and bars, would be better. Buenos Aires is a great city so you will enjoy it wherever you stay!