I hit a number of Christmas markets in the south last year and have also done so in the past. A few comments:

I found Nuremburg to be extremely overrated. Very touristy and visitors from China would likely have recognized most of the products, having made them.

Munich has long been one of my favorite places for the markets. It continues to be, though they do vary a fair bit, as there are a goodly number of them (especially if you count all the little neighborhood ones).

My all-time favorite is one I found this past year in Regensburg. It was in the courtyard of the castle of Thurn und Taxis and was absolutely lovely. The site was nice, but the ambience was better. I am not certain, but I think it was open only in the evening, which added much to the ambience, as they were trying to go for a historical effect. They had a couple of bon fires to stay warm by, a lot of the illumination was also done with fire. It was very pleasant. Also nice was that not all, but I would say most of the goods were hand-crafted. They even had a few artisans there doing their thing -- a woolens stand had a woman spinning; there was a wood carver making small wooden ornaments, etc.

Close to FRA is the little medieval town of Michelstadt. I've not been to their market, but it is high on my list for ones to check out -- the town center has been nicely preserved and I think it should make for a fantastic backdrop for a market -- if they don't screw it up. I'd love to hear if anyone has made it to that one and if it is as nice as it could be if done well.

The Christmas markets are wonderful. Have a terrific time!