We are going to Berlin for 5 nights in May. Any advice on the best areas to stay. We don't mind taking public transportation but it would be nice to be able to walk too. I haven't been since 1986 before the wall came down. All suggestions of what not to miss is appreciated.
You will experience a nearly total different city than 1986. I dare to say that Tiergarten, Victory Column and the Memorial Church (all in former west because 1986) are the only things that did not change.
Area: choose a hotel around S station Friedrichstrasse or (in May) a nice hotel near Tiergarten.
You will need public transport: U + S map and journey planner. Or choose BVG Fahrinfo app.
Without knowing your interests it is hard to say what you shall not miss besides the top 10 of Berlin. Visiting Reichstag needs an early reservation including passport. For a first day a HoHo bus takes you to main sights and gives a good introduction.
Please allow me as time witness to comment that the Berlin Wall was opened (not falling or coming down), initially by Harald Jäger, a local border guard officer at Bornholmer Strasse. And the opening was only one-way: in the first weeks citizens of the western part of Berlin (part of FRG) still needed visa to travel into the eastern part (state of GDR). I still have the rest of a ten-card card visa to avoid single visa applications.
When I was there in 2022, I stayed in Hackescher Markt, at the Adina Apartment Hotel Hackescher Markt. My room was a studio since I was by myself but they also have 1-2 bedroom apartments with fully equipped kitchens, washers and dryers and so on. They do have hotels in other Berlin locations as well, but I personally really liked this location. The staff was friendly and courteous, and the rooms were very well prepared, large, clean and nice. Breakfast is available although given the kitchen facilities, I just ate in my room in the morning.
But the best thing is that the location is an easy walk to many major sites. The DDR museum is only a few blocks away, along with the TV Tower, and Museum Island is a quick 5 minute walk. You can easily walk to Lindenstraß from there. It is also very convenient to the U-Bahn, S-Bahn, and trams. There are several grocery stores a few blocks away along with a couple of wine shops, many cafes and good restaurants. I would definitely stay in this location again.