We had a very nice stay in the Singer Hostel. The hostel is close to the subway station and only 1 station away from Alexander Platz. All places in Berlin we wanted to visit were easy to reach. The room was very clean. Soap and towels were available.
The only thing we were not so happy about was the noise in the evenings. The walls in between the rooms are quite thin, so you could easily hear the neighbours talking and playing music till later at night.