I have stayed with a friend at Martin´s appartment . It´s close to Public transport that takes you whenever you want to go in Berlin or also can walk because some turistical places are on walking distance. The appartment is nice, clean and really big and comfortable. On wednesdays and saturdays there is a fruit and vegetables market just in the corner of the building with incredible fresh and cheap products!, I recommend Martin´s appartment and if I had the chance to go again to Berlin I will try to stay at this place for sure!