Normally it is the best to use the public transport(bus, tube and ship). But you should not miss to take a car and drive over the Köhlbrandbrücke(see at the picture). You have a wonderful viwe over the harbour and the city.
Hamburg has the second largest dock in the world. and as you are cruising down the river coming into dock this is one if the views to your left, teh suspension bridge, its Massive!