I visited Berlin with a friend for a long weekend. We chose Nena Apartments for its closeness to the Berlin public transport system. It lies quite conveniently and there are metros every 5 minutes to all parts of the city (but we happened to stumble upon the other Berlin location and that one is located even more conveniently).
The apartment was clean and tidy. The bathroom even had a "waterfall" shower head (but we had to figure out how to get it to work: pull a small ring just under the water hose and it will switch to the larger shower head).
Also, the kitchen was well-equipped in terms of machinery: it had a toaster, a coffee machine (Nespresso, although they only provided 2 cups...), electric tea kettle (also ideal to make on-the-go tea or coffee if you make day trips). There even was a small dish washer that fits just enough for 2 person's dishes! The only thing missing was like a rag to wipe the table or kitchen counter after use... Not a really big deal though.
In terms of noise and comfort: quiet neighborhood (a little shady, we avoided going through the park late at night, but in retrospect almost all of Berlin is quite deterioratedq). The apartments have a "quiet after ten PM"-policy, but you do hear people coming into the hallway if they are loud (it woke me up once or twice). Also, the room was quite hot (thermostat set to "4", which we obviously quickly turned down), so we had to sleep with the window open. Sometimes, there are cars making a lot of noise in the neighbourhood and you will hear that as well.
That's about it! I would recommend it, but I also think there might be better / more interesting places around the city.