I tend to like Dusseldorf but absolutely love Cologne. One of my favourite cities in the whole World.

Both have their attractions, interesting museums, the Medienhafen in DD and Rheinauhafen in Cologne for architecture, fine restaurants and nightlife.

Also plesant green spots, parks, ponds that invite for a relaxing walk or run. Baroque castles at Benrath and Bruehl surrounded by sophisticated gardens.

And of course the stalwarts, Cologne cathedral, the Altstadt in Dusseldorf, 4711, Koelsch and Altbier...Not to forget Bonn, Koblenz and other interesting towns in the vicinity.