I highly recommend stay at Ivos's apartment.
First of all, the apartment is located only 2-3 minutes walk from S-ban and U-ban. The major sightseeing places are easy access from the apartment such as Museum islands, berlin dom, Brandenburg, East side gallery and Reichstag). I can take 100 and 200 public tour bus at alexanderplatz (one S-ban station from Ivos's apartment).