First time in Berlin, need neighborhood advice

Here are 3 recent threads on this subject that may help you. I stayed at Pension Peters in the Charlottenburg neighborhood and found it well located for getting to all the Berlin sights by public transportation (U-bahn, S-bahn, bus). It's conveniently located between two stations - Savignyplatz and Zoolischer Garten, from either of these you can easily get wherever you want to go. It's in a nice neighborhood with several restaurants and shops and it's pleasantly quiet compared to some other neighborhoods while still being on major thoroughfare.

https://community.ricksteves.com/travel-forum/germany/choosing-an-east-berlin-hotel-vs-west-berlin-hotel
https://community.ricksteves.com/travel-forum/germany/hotel-recommendations-for-berlin
https://community.ricksteves.com/travel-forum/germany/berlin-hotel-d9966f2e-e1d0-43e4-b188-cb3ea5098dbb

"...which neighborhood?" I stay at Savignyplatz but not at Pension Peters. That's located close to the corner of Kantstrasse and Savignyplatz. True it is a very convenient area, numerous restaurants of various cuisines, grocery stores, internet cafes, and the closest S-Bahn station, "Savignyplatz," from which you can reach Potsdam and Berlin Hbf direct in the opposite direction. Savignyplatz is located in Berlin-Charlottenburg if you prefer staying in the west.

To get to Berlin Cathedral (Berliner Dom) and Museum Island, the Brandenburg Gate, Checkpoint Charlie, you take the S-Bahn going east, get off at Bahnhof Friedrichstrasse, and walk a few blocks to the Brandenburg Gate. When you reach Unter den Linden, you'll see it, the immediate eastern side of the Gate is Pariser Platz.

We stayed at Pension Peters and found it to be in a very good location.

I stayed at the Mercure Checkpoint Charlie. While I often took the U-bahn, it was walking distance to many sights, quiet, and less expensive than closer in to the center.