Southern Germany, maybe a visit over to Salzburg?

I suggest that you get out a map of southern Germany. Your plan to do the Romantic Road is good.
https://www.romanticroadgermany.com

Make sure that you include stops in Dinkelsbühl and Nördlingen as well as Rothenburg ob der Tauber. Those two towns have the medieval walls and not so many crowds like Rothenburg. Augsburg is worth a half day to see the Rathhaus and Die Fuggeri.

The Romantic Road doesn't go through Munich. However, after following the road down to Fussen and Garmisch, cross over to Innsbruck, Austria then head east to Salzburg, Austria. Then head up to Munich before heading down to see the Bodensee (Lake Constance) the Rhine Falls and Black Forest. Then up to Frankfurt. Driving would be much better than the trains, especially doing the Romantic Road and then the trip from Munich to Lake Konstnaz.

Welcome to the forum.

"Where should we drive about/where makes more sense to train?" First, some thoughts on your itinerary.

It gets said very often on this forum, but the Romantic Road itself isn't very scenic and maybe not as special as it sounds. The RR is actually a tourism marketing scheme - a very successful one - that lures a lot of visitors - too many at times - onto a single north-south driving route. It's not just one road but a series of many different roads that connect certain towns, most of them attractive towns, but for certain, towns that have signed up to become RR members (and that pay annual fees of around €15,000) so that the "Romantic Road" moniker will attract more tourists and Euros to their town.

So... the real unspoken truth about Southern Germany is that there are MANY nice old-world towns all over the place. They obviously can't all be "Romantic Road" towns for different reasons - they may be a few miles, or a hundred miles, too far from the RR route. Or they may not be willing to cough up a €15,000 fee every year. Or the townsfolk may not want to deal with all the traffic and troubles that tourism can bring; there are in fact some towns so overrun by tourists that the locals feel invaded and are looking for ways to turn them away.

As you can tell, I don't consider it a necessity to drive the entire Romantic Road. It's a better strategy, I think, to consider the things you like to see and do, and visit those kinds of places as you make your way south. You MIGHT want to include some RR towns if they meet your own needs and suit your interests. Read up on them and see which ones look interesting. One that suits me a lot is Nördlingen. But you have your own interests... Are you into wineries? Maybe a place like Sommerhausen or Iphofen would suit you. If you are interested in truly well-preserved old-world towns, then maybe Bamberg or Regensburg - both UNESCO World Heritage sites - would be good. Bamberg, btw, has a famous and well-developed beer culture. These places weren't as heavily destroyed in WW II as now-touristy Rothenburg was (about 40% was rubble.) Bad Windsheim has an excellent open-land cultural museum if you want to learn about local life in the area. Want to enjoy the outdoors on a bike ride? There are lots of place, but the Altmühl River Valley near pretty Pappenheim is nice for that. None of these places are on the Romantic Road - and all are less impacted by the tourist horde than a place like Rothenburg.

Rick Steves emphasizes both the RR and Baden-Baden in his materials. Overemphasizes, IMHO. B-B is good for casinos and spa treatments - so might be right if that's what you're into - but there are dozens of other great places to visit in the nearby Black Forest and the broader region. A nice old-world base town for visiting the BF and Strasbourg (FR) is Gengenbach, located on the scenic Black Forest Railway.

cadogan111, if it were me, I'd look at an open-jaw air itinerary: into Frankfurt and out of Munich. But I'd skip Baden-Baden, add Salzburg, and I'd do it all by train. I know many people prefer to drive, but the roads are just roads, and the Autobahn is just interstate highway without billboards. All the places you've identified are reachable by nice comfortable trains. Alternately, for a first visit, I much prefer the Rhine valley than Bavaria.

Thanks for your travel tips! Will help in planning our itinerary.