Heidelberg Christmas Markets

Bad Wimpfen
Mannheim

Heidelburg is just over an hour from me, and a weekend shopping destination, so I have some recent experience with what you've got within an hour by train. Here are some to consider:

Mainz - good, easy to get to, large and spread out with lots of other stuff in town to see. https://www.mainz.de/freizeit-und-sport/feste-und-veranstaltungen/weihnachtsmarkt.php

Neustadt (Wienstrasse) - small city in the heart of the Pfalz wine region. Market starts right by the train station (normally, but that area is under construction right now and I don't know if that will be done in time). That being said, I like this town. https://www.neustadt.eu/Tourismus-Wein/Top-Events-Aktuelles/Weihnachtszeit-in-Neustadt/Weihnachtsmarkt-der-Kunigunde/

Bad Durkheim - Really good and not on most Americans radar. Wine country central (site of the biggest winefest in Germany). Very attractive old town to wander through. https://www.bad-duerkheim.de/kultur-tourismus/veranstaltungen-feste/duerkheimer-advent/#/veranstaltungen

Frankfurt – I have not been for a few years, but it’s on my list for this year. https://www.visitfrankfurt.travel/erleben/feste-und-veranstaltungen/frankfurter-weihnachtsmarkt

Rudesheim – Very much a tourist town. Take the train to Bingen and the ferry across the Rhine. I’ve been, but once was enough. https://www.ruedesheimer-weihnachtsmarkt.de/

Worms – Kind of a strange town, it’s a stop for the tourist boats, but there’s really not that much to see. https://www.worms-erleben.de/erleben/erleben-und-feiern/veranstaltungen/worms-im-advent/index.php

Speyer – A really good town to walk around, great cathedral, good history museum (not cheap), and fantastic Technology Museum! Good market too. https://www.speyer.de/de/veranstaltungen/weihnachtsmarkt/

Bad Kreuznach – mostly a German destination, this market is only on weekends. https://www.bad-kreuznach-tourist.de/kultur-geniessen-und-einkaufen/weihnachtsmaerkte/

Landau – This is more of a local handicraft market, with a lot of regional booths. Landau also is a good place to spend a day. Very good Roman history museum. https://www.leichter-reisen.info/regionen/suedliche-weinstrasse/veranstaltungen/kunsthandwerklicher-thomas-nast-nikolausmarkt

A bit further out (2+) hours by train):

Trier – Excellent town to visit, great history and easy to walk around, excellent shopping, very good Christmas market. https://www.trierer-weihnachtsmarkt.de/

Saarbrucken – The old part of this city is really nice and full of shops. The Christmas market is good, but Mainz and Trier are better. https://christkindlmarkt-sb.de/

Koblenz – Really worth a day, this is a good town to see, the Eck is the major attraction, the Christmas market is good, but even better is the Winter Garden at the fortress. https://www.koblenzer-weihnachtsmarkt.de/ + https://www.christmas-garden.de/koblenz/

Wiesbaden – this is an expensive town, with a large American population. Not the best market, but everything is top quality (and so priced). https://www.wiesbaden.de/microsite/weihnachten-en/index.php

Ones I’d pass on:

Kaiserslautern, Ulm, Heilbron. Been there, not impressed.

Possibly worth doing if you have the time: Wissembourg, France, which is easily reached by train from Heidelburg. Very pretty town, good market. https://www.visit.alsace/de/219005601-weihnachtsmarkt/