Our stay in Milenas appartment was just perfect. It is located within 5 min walking distance to the next U-Bahn and Airport Train connection. You can also reach many excellent restaurants by foot (20-30 min), but you could also use the well-equipped kitchen of the appartment to cook your own food. All the rooms were super-clean and we had more than enough space for a 5-day city trip. Milena is very friendly too, knows the city, provides clear check-in instructions and is also flexible regarding the check-in times.
One thing to know is that the wall separating the shower from the bedroom is semi-transparent, making it slightly less ideal for business trips (if that is what you are planning for).