When clients ask me about which neigbourhood of Berlin is best, I really do not have a definite one-word answer. To me, the diversity of Berlin is the beauty of it: anyone can find a place that fits his lifestyle and preferences. It is not a city where you could just pick a street in the city center close to the Brandenburg Gate and consider it done. There are at least 5 neigbourhoods of Berlin that I consider in my list of favorites, and investing in an apartment in any one of them is good. Choosing the right neigbourhood would mean settling for a certain lifestyle, history, neigbours, and entertainment options. Therefore, I would like to help you by giving my personal feelings about each of the top 5 neigbourhoods: Charlottenburg, Mitte, Prenzlauer Berg, Friedrichshain, and Kreuzberg.
Before you decide which neigbourhood of Berlin is your favorite, you should understand the history of urban development in Berlin, which is quite unique due to the fact that the city was divided throughout most of the modern history, between 1961 and 1989. The Berlin Wall created something unique from the Urban perspective, which no other European capital experienced: the city had two cities within it, Berlin East and Berlin West. Each with its cultural and entertainment 'city center', with its own opera, with its own museums and its own shopping streets. Today, these areas are divided by Tiergarten - the biggest city park.
After the reunification of Germany, the two separate, independent and fully developed urban areas had to create a synergy together again. Therefore, today, you really have 3 city centers in Berlin: city center West (around Kurfürstendamm, Savinyplatz and Wittenbergplatz, which belong the neigbourhood called "Charlottenburg"), city center East (around the TV Tower, Alexanderplatz, Berliner Dom, Hackerscher Markt, Unter den Linden, which belong to the neigbourhood "Mitte").
Since the Wall came down in 1989, there has again been great competition between Berlin’s various centres, and it is this variety of Berlin which is the beauty of the city.
So, if you are looking for a residence building or a commercial unit on a good location on in the city center, you have to be aware that both City Center East and City Center West can give you similar value.
Further to this should be said, that Berlin as we know it today, has been unified from several single townships in 1920, which created Greater Berlin. The townships have then become Berlins neigbourhoods which means that every single neighbourhood of Berlin will have its own instructucture for comfortable living: shopping areas, restaurants, bars, parks, schools, entertainment, creating a special feel of a sub-center. This means all areas are busy both in the day time and at night.