traveling from Dresden to Poland mid December. Deciding between Warsaw or Krakow. Suggestions?
If you are coming from Dresden then the most obvious choice is Wrocław. Other than that it depends on your interests.
They both have a lot to do and see, so as qq said, it depends on your interests. Without any more info, I'd guess most people think Krakow is much more interesting, especially the old town. Warsaw is a bigger, more cosmopolitan city, and lost much of the historic architecture in the war. Still worth seeing if museums and monuments are what you're interested in.
Are you visiting for the Christmas markets? Many videos covering those on YouTube. I would research Xmas markets for each city.