I will be landing at 10am on a Thursday from the USA and then leaving for Vienna on Sunday for 4 days . Is this enough time to see the highlights and what the no miss sights. Thanks!

4 days in Berlin is fairly enough to see the major sights and the museums.If you plan your schedule well maybe you can even squeeze in a trip to Potsdam just outside Berlin. Try to stay in a hotel in the Mitte district so it would be convenient to take public transportation around the city, though taxis are pretty reasonable. Berlin is easy to navigate. Suggest you get day passes to take unlimited rides on bus #100 or 200 which goes around the major sites such as Berliner Dom, Reichstag,Brandenburg,Potsdamer Platz,etc. You can get on and off the bus anytime to explore. If shopping is your fancy, try to visit the KaDeWe department store. The 6th floor has various dining places offering varied cuisines and a large food shop selling all sorts of foodstuff and delicacies. My daughters and I had a lovely time when we visited Berlin 2 years ago.

Do a search for "Berlin"..there are lots or recommendations to include hotel locations.

IMO with the excellent public transport system you do not necessarily have to limit your hotel possibilities to the Mitte area.

Berlin and Vienna will be a great combination of cities. Each a capital and yet very different. Tons of history and culture to see.

As for Berlin, what you do will obviously depend on your interests. What do you like: WWII history? Cold War history? Palaces? Art? Music? You will be pressed in Berlin, given that your first day, Thursday, will be jet lagged (and I assume that Sunday will be a travel day, not any sights). I'd suggest that your arrival day would be a great day to walk and see the main sights of central Berlin: the Brandenburg Gate, the Reichstag, down Unter den Linden (walk or bus) to Gendarmenmarkt and Museuminsel, ending at Nicolaiviertel.

Let us know what your specific interests are, and it will be easier to make suggestions. Also, what time of your you will be there.

If you search for my name, you'll find a recent Berlin trip report. There is a ton to see there, and you won't be able to see everything. You will have to focus a bit. I loved Vienna as well. Both have amazing museums, but you may want to split it up a bit (i.e. maybe you don't need to visit both Berlin's Germaldiegalerie and Vienna's Kunsthistorices).