Singer109 was an awesome hostel.
Often hostels get a bad wrap for being dirty and not well-kept, however Singer 109 was clean, the staff were kind and helpful, and the aesthetic of the inside foyer was fantastic.
Only trouble is the moderate distance from Alexanderplatz. It really isn't too far, I walked to the square every day, it took me about 15 mins to get there - from there it is easy to get trains around the city.