We would like to travel from Krakow to Hamburg, preferably by car. Is it better to rent a car in each country or rent in Krakow and drop off in Hamburg? Thanks for your help!
You can get a few price quotes (e.g., start with Kemwel or Auto Europe) and will usually find that a dropping a rental in a different country adds several hundred dollars to the price. It can be cheaper to rent two separate cars and take a train ride in between. If you'll spend a few days in Berlin or another city where you don't need the car, then maybe that's the spot where you train in and later get a new car (or even stick to train, since service around Germany is extensive).
If you decide to do this route by train, the bad news is there is no straight shot Krakow to Berlin anymore, which I took in 2001. Now, you have to change in Warsaw. The most convenient way is Krakow-Warsaw, Warsaw to Berlin, (stay a night), then Berlin to Hamburg on the ICE.
Depending on the dates. It would be about $50 each through EasyJet for a oneway flight
DB Bahn (German railways) also runs a Krakow-Berlin coach connection. From Berlin, you can connect on to Hamburg.
You can do this all on one ticket, and take advantage of their "Europa-Spezial" discount fares. A Krakow-Hamburg ticket would start from 39€.