Funny, I try and see a new market every year, and get a new mug...
I loved the one in Freudenstadt, even though it's only a small one.
Since it's in the Black Forest, the chances for snow are pretty good, too.
The one in Esslingen (near Stuttgart) we visit every year, since it's got a medieval part to it, which is really cool.
The one in Nuremberg is very famous, even though I have not been there, yet.
The one in Stuttgart is the largest in Europe, as far as I know, can't promise snow, though.