Frankfurt, Mainz or ?

It depends on the other Christmas markets you want to visit besides Bacharach (they only have their market on one weekend) There are many small towns that have great markets, but again, maybe just on one weekend, like Büdingen or Idstein. Limburg, Marburg, Seligenstadt, Michelstadt and Bad Homburg are longer markets and well worth adding to your list. All are easy to get to from Frankfurt and it may be the better train hub for you for many destinations.
Where are you reading reviews about staying in Frankfurt? The market there is wonderful and there are many other sights to see there besides the market. (museums, medieval churches, Jewish cultural sights, etc.)

I would not stay in Offenbach. Otherwise, Frankfurt, Mainz or Wiesbaden are fine.

I just got back from a boat trip along the Main for the Christmas Markets. We started in Frankfurt and ended in Nuremberg.

We had an excursion to Weisbaden. To be honest, I would choose Weisbaden over Frankfurt. it was such a charming town, the Christmas market was better organized and had more unique offerings. Away from the markets, we discovered so many cafes, wine bars, charming shops, and such a quality, local vibe.

Wiesbaden is known as "old money" town and the capital of Hessen state (although Frankfurt is much larger). Therefore it has a very good quality of life.

Be aware that Mainz - also partly attractive - is located along the east-west oriented runways of the airport. Depending on wind you can see and hear partly starting or landing planes.

Since you mentioned "Heidelberg, maybe Stuttgart" I like to mention Darmstadt as well which has a very science oriented offering. The bus Airliner brings you directly and comfortable from the airport to Darmstadt. And of course you know that chemical element Meitnerium was first explored there. :-)

Thank you Ms Jo -- always appreciate your guidance! So helpful to know certain markets are only on weekends or only 1 weekend. Will do some further research and appreciate the additional markets to visit. I will definitely add/modify my planning. I think I read the adverse feedback on Frankfurt somewhere in this forum. However, my hubby and I visited Frankfurt years ago which we certainly enjoyed. Frankfurt is such a great hub, too. Thank you! We'll plan early so we can find an apartment for 6! Ha!

Thank you also MoR --Weisbaden looked interesting, too.

And thanks MarkK ...interesting regarding the science-this requires more investigation!

Wiesbaden has the advantage of being a spa town, so you can warm up in a hot pool!

Rüdesheim, the gateway town to the Rhine River Gorge, will have a month-long Christmas market from Nov. 20 - Dec. 23. It's a fairly large market with great old-world atmosphere and is strung out around the town in a pleasant way.

Layout: https://www.ruedesheimer-weihnachtsmarkt.de/wp-content/uploads/2024/11/Uebersichtsplan-2024.pdf

The cable car ride to the Niederwald Monument is open throughout the Christmas market:

https://www.seilbahn-ruedesheim.de/en/

Mainz's market is large and fun too. It ran from Nov. 28 - Dec. 23 in 2024. Not sure about this year. And of course Mainz is a city with much to offer at any time of year.

To the north of Mainz and Rüdesheim:

Koblenz has a "Chrismas Garden" at Ehrenbreitstein Fortress (use the cable car) as well as a more traditional Christmas market. In 2025 the market runs from Nov. 22 to Jan. 5.

Tiny Braubach (just a few minutes from Koblenz) has a one-weekend Christmas Market around the first week of December in its very handsome market square. But the town has some handsome buildings (year-round of course) and is home to Marksburg Castle (which offers year-round tours.)

You can see on the map below that all these Rhine destinations are within easy striking distance of each other. If you were to stay in MAINZ (closest to FRA airport /"Flug" on the map) or Rüdesheim, you could easily visit them all. Frankfurt proper, if that interests you, is about 40 minutes from Mainz.

https://www.seat61.com/images/rhine-train-map.jpg

And from Mainz you can easily catch a train when you leave the area to Heidelberg, Stuttgart, or Basel.

Thanks G3rryCee and Russ...lots of options! I appreciate your recommendations. Now will be the challenge to find a 3 bedroom 2 bath apartment - for the 6 of us!!

Find the apartment. As long as it is near the train station in any of the mentioned towns/cities you will be fine

The two cities that are train hubs central to the sights you list are Mannheim and Neustadt (on the Winestrasse). Both of these are less than an hour from Frankfurt, Mainz, Wiesbaden, and the Rhine, as well as Heidelberg. Stuttgart is just a bit further, but certainly closer than if you base near Frankfurt.

Both of these cities also have Christmas markets, although I wouldn't make them primary destinations for such. Mannheim is an industrial city, not very touristy, with some sights worth visiting, but probably best in Spring when it's not so grey. It is a major transport hub and has many trains daily, so that gives you a lot more choice of movement. Neustadt is a wine country destination, and very touristy in the summer and fall, and has a large number of places that cater to tourists with food, drink, and lodging, as well as being a very nice, walkable, city.

My preference would be, between these two, Neustadt over Mannheim, but you should be able to find a very reasonably priced place to stay in either.

Agree with Stephen. Find the apartment first.