We have been to Gdańsk krakow Warsaw which of the above would you suggest to stay for 3 days in January? What would the weather be then?
Rhetorical question. Wrocław of course.
I'd also vote for Wrocław, but I don't consider the question rhetorical, Poznań is a great city as well, so if you for example find cheaper/better flights to Poznań, then go there. Both are full of history and have very nice old towns and market squares.
warsaw, has by far the most to offer to distract you from the cold
+1 for Wrocław