Went last Christmas to Berlin and to their markets, again tap up Herr Tubthumper he will point you in the right direction, for me the best one was the central one, Gendarmenmarkt Christmas Market, it was great and very Christmassey.
https://www.youtube.com/watch?v=6UQyND_WvDM
Quite surprisingly last year was how quiet it was, expected a more 'Berlin vibe' but it wasnt happening, I suspect we were always a wrong turning away from party town, but didnt find it ....
Let me know if you're over again because I certainly know the party places.