Hamburg or Lubeck?

My tip - without knowing your interests in detail - is to spend 3 nights in Hamburg and one in Lübeck or Travemünde (e. g. on old Passat ship).

Lübeck is really fascinanting and had its glorious time before Hamburg with Hanseatic League.

Northern Germany has also some other interesting towns and places, e. g. Harz mountains with old town of Goslar, Lüneburg, Bremen, Schleswig with Viking village Haithabu, the beautiful coastline, unique Isle of Helgoland (ferry day trip from Hamburg), Laboe and the old original WWII submarine with huge memorial, ... just to name a few highlights in the former western part.

I've only been once to either, but that was last Autumn so they are reasonably fresh in my mind. Lubeck is smaller and, at least in the (tourist), centre, more "oldy worldy" (although I was surprised how much was ugly, post-War building). There is enough to see that would easily fill a day or perhaps two. I especially recommend the newish League museum and taking a boat trip around the city. So, four nights there wouldn't be unreasonable, especially if you are taking a day-trip to Hamburg. We were actually in Lubeck for four nights, although one day was a trip to Eutin (great, highly recommended) and another morning was in Travemunde (dull).

Hamburg is, obviously, much larger (and, in my opinion, much more interesting). It has many more tourist sights and considerably more variety compared to Lubeck. We didn't see everything with 5 nights in Hamburg - admittedly we are very lazy tourists - but really enjoyed what we did cover including a number of interesting museums covering various periods (also, especially liked the the port tour & walking harbour areas - plus Miniatur Wunderland, which is brilliant!).

Personally, I'd stay in Hamburg for its varied sights, with just a day-trip to Lubeck for a middle ages/Hanseatic League fill.

I can share our experience on a Baltic cruise we took a couple of years ago. We had two full days in Hamburg and one fairly full day in Lübeck. In Hamburg, we spent a full day walking around, including the warehouse district, the park with lakes, a beautiful shopping street for cafes, Min, Wunderland and more. ( We were good with about 1 1/2 hrs with the miniatures; we met several who spent hours there). Quick paced and probably shortchanged, but the second day we took the train to Lüneburg and had/have no regrets, as we think it was one of the most beautiful places we’ve ever been in our many years of travel. Lubeck had many beautiful and interesting buildings dispersed among a lot of not as interesting. The day was well spent there. I am pretty sure we could not have spent four days in Hamburg, however. Nor in Lübeck for that matter. I’d consider transportation ease for a day trip or two based on MarkK’s expert suggestions. Hope it all works out. We enjoyed our time there a lot.

Northern Germany is a pretty underrated area in my opinion, Hamburg and Lübeck are both lovely and I can really recommend them. I would even suggest cutting down your stay in Bacharach with a night or two and add them in the north (or spend a night in southern Denmark). Hamburg is a big city with a lot to see, the Miniatur Wunderland alone takes a full day and there are several other museums and sights. For some less conventional things to do you can take a tour of the Airbus factory in Hamburg or a boat tour of the port (third busiest port in Europe, not what you would expect from a city over 100 km from the coast).