Munich or Frankfurt as home base for day trips for Christmas markets

There are many wonderful markets in smaller towns near Frankfurt, though some of them depend on when you are here. Büdingen and Idstein are only on one weekend during Advent. Bad Homburg only has their market on weekends. Seligenstadt only goes til mid Dec. Michelstadt is only Wed. through Sun. Limburg and Marburg are on during all of Advent. Mainz and Wiesbaden are also great markets. The market at Hessen Park Open Air museum might be of interest to you too, as this is a great place to visit at any time.
In Frankfurt, you can also go to the market in the City Forest, which is rather unique.

Marburg was the only one you mentioned, but the markets in these other towns are wonderful and full of charm.

Storybook towns and castles... with just 7 days, basing in cities the size of Munich or Frankfurt, where you will spend a fair amount of your time, achieves the opposite in terms of atmosphere. Also, some of the daytrip destinations (like Rothenburg) border on undoable because of the travel time involved. You can fly into one of those two airports, but then I suggest you travel to a smaller city and stay there.

Nuremberg comes to mind first and foremost. It has a walkable and atmospheric old town zone - and its own castle - and it is great for taking easy day trips to the old-world towns of Regensburg, Rothenburg, Bamberg (which should definitely be considered,) as well as Bayreuth and Veste Coburg. Then again, there's also Amberg and Iphofen (teeny-tiny storybook) to consider as well. And if there's something you need/want to see in Munich, you might do that city as a day trip, or perhaps as a stopover on your way back to MUC airport prior to your final night in Germany.

We lived in Augsburg, Germany for four years (50 miles west of Munich) and loved Bavaria. We always enjoyed the Augsburg Christmas Markets, never visited others, but the one in Nuremberg was well known for being the best. That was 30 years ago, not sure today,

Still, I did my Army Reserve duty frequently in Frankfurt and visited the areas you mentioned as well as other Rhineland areas.
To me the two best areas of Germany for touring are Bavaria and the Rhineland. You can't miss either way, but I strongly recommend Bavaria.

Within an hour of Frankfurt you have over 100 Christmas markets. There's 1400 in the Rhineland alone. Many only run weekends or for one week. There are also over 80 castles in that same area. Some are wrecks like Rheinfels, some are still lived (Burg Eltz), some are just huge (Ehrenbreitstein). Plus you have the wine regions of the Rhine and Mosel. So that's a good place to base from.

Munich is okay, but you'd do better to base out of Nuremberg if you want to do Rothenburg and/or Regensburg. I say this because you also have Wurzburg, Bayreuth, Bamberg, Amberg, and Munich within an hour by train. Plus hundreds of smaller places, Like Ansbach, or Nordlingen, or Crailsheim. And yes, there are castles there too.

The thing is, and don't get me wrong, the big cities are really good for the markets, but if you really want the small villages you need to ignore a lot of the advice you'll get here. That's because tourists don't go places like Bad Homburg, or Deidesheim, or Trippstadt. Wissembourg is beautiful, has a decent amount of the old fortifications left, and has a very pretty Christmas market. And I can go and be the only American in the town.

I was in Metz today. Really good Christmas markets. Great sales in the stores. Fantastic food (oysters, tartiflette, frog legs, snails, sausages, wines, hot chocolate, etc.). I heard one other person speaking English. But it's not a town that gets a lot of tourists. Trier is the same, fantastic history, really good market, great shopping, Roman ruins, and tourists prefer Rudesheim (which isn't all the good). And those are cities. Go to Bad Windsheim for the Medieval Christmas market and the only Americans you'll see will be from the airfield 10km down the road.

Here's a link for some of the markets. You'll need to get the dates next year later. But realize this is nowhere near all of them

https://www.brunnvalla.ch/christmasmarkets/germany.html

I appreciate everyone’s detailed responses and recommendations. It’s given me some direction for further research for the trip.

Munich plus 1, maybe 2 day trips would be my plan.

There are some wonderful old castles near Frankfurt that are not on the Rhein, in towns like Kronberg, which is a very old, original Staufen castle. Eppstein and Königstein have castle ruins, but they are fun to walk around in and all 3 towns have a Christmas market on one weekend.

Ronneburg is an original castle near Büdingen and they have a medieval market on 3 weekends during Advent. Those who like the Marksburg, would like Ronneburg as well as the castle in Kronberg.

The palace in Bad Homburg is an original palace left from the Kaisers and has beautiful rooms to see. The market here has the most hand made items I have seen at a market, except for the medieval markets at Ronneburg and at Esslingen near Stuttgart.

Am not a fan of the Rüdesheim market. It used to be quite international, but the last few years, it is mainly just Chinese items. Lots and lots of Chinese items. Saw a Norwegian stand, a Mongolian Yurt, Polish Pottery and wood items from Yemen. The chair lift saves this market as the view at sunset is stunning.