The Singer 109 hostel was one of the most clean hostels I have ever been. It is very welcoming, cozy, and well maintained. It is located in a very quite and safe neighborhood (15-20 min walking distance from Alexanderplatz). They offer everything that a tourist may need for an additional charge (about €2). The staff is quite friendly and helpful, and they speak multiple languages. I personally came across guests of all ages from all over the world. During my stay, I was lucky to enjoy a quiet night there. No noise at all. I did not see any AC but luckily the temperature in the room was cool enough. The hostel offers buffet breakfast for additional €5 , which is great and saved me a lot of time looking for a breakfast place. The espresso I had there was amazing, Italian style, short and very strong. They even have happy hour.
If you are looking for privacy and solitude, this may not be your place. Keep in mind that the bathrooms and the bedrooms are co-ed, but at the same time everyone is very respectful toward other people's privacy. This is the only "inconvenience" but it is worth it for the rates and location.