Train vs car rental in Germany

The German train system is near-perfect and can be very cheap. If you, as you do, know your itinerary advance-bought tickets come with a huge discount. For a group like yours travelling on intermediate distances is a real bargain with regional tickets: Rothenburg to Munich is a mere EUR 43 total.
Check at the website of the Deutsche Bahn the connections and prices for your intended travelling days.

I'll just say that rail travel in Germany is easy and convenient. The places on your list are very easy to reach by train. Consider that when comparing driving to rail, don't forget to think about fuel costs, parking, and the stress on the driver. Rail tickets can be fairly inexpensive if bought in advance or with the variety of regional and local passes. The German rail site, bahn.com is your best source for info and the site "man in seat 61" is also worth looking at for guidance.

I agree - the German trains are great. I took them from Paris to Berlin (with detours) across Germany over a few weeks some years ago. I love trains so it was fun - I always default to train travel in Europe and look for alternatives when trains aren't practical. If you don't love trains so much, though, it might not be a horrible idea to rent a car.

As a compromise, you might rent a car just for a short time and take trains the rest of the time, if say there's an area where you might prefer the flexibility of a car. (Although it was easy for me to get to Rothenburg ob der Tauber by train, it's not right on a main line, so you need to detour a little to get there, a couple of changes perhaps, which is where a car might make it a little easier.) I sure wouldn't want a car in a big German city. But there's no need to go all or nothing with all driving or all trains.

Since the train system is good, I opt for the train for the most part, and I even started doing that when I was traveling for business, since it seemed like I could always get within walking distance of my hotel on the train, then visit the client with a taxi. Took a lot of stress out of traveling, and saved my employer some bucks to boot. I do rent a car when I want to get somewhere the trains are not convenient. In your case, there is frequent train service to every where you are going, special day tickets so you can travel cheaply as a group.
Here is the relevant website for these tickets.
https://www.bahn.com/en/view/offers/regional/index.shtml?dbkanal_007=L04_S02_D002_KIN0060_ST-REGIONALE-ANGEBOTE_LZ01

I am very glad to hear that we'll be fine w/o a car, public transportation was one of the things I really enjoyed in Italy. I bought in advance then and will now too, I was surprised at how inexpensive and convenient it was. Thanks everyone for your help!

Mass transit is usually pretty good, allows you to travel without hassle. Renting a car gives you the convenience of going when you are ready & ease of getting to areas off the main routes. Driving in Germany is much the same as in the US; if you rent, read up on the rules of the road and you should be fine. Both travel options have advantages. Enjoy your trip!

Trains are great, especially for pre-planned trips between cities. But outside of cities, and especially with four people, Germany is a great place to rent a car - great roads, no tolls. For instance, along the Rhine River - 'let's go to the next town for dinner, or because the next town has a nice big grocery store, or...'. with a car, any or all four of you can do that spontaneously and be there in ten minutes for essentially no additional time or cost. If you are stuck to train, it means walking to the train station, buying tickets, waiting for the train, checking the schedule to see when the train comes back, etc, etc. Have you ever rented a car in the US? Renting a car in Germany is just as easy and provides great flexibility outside of cities. For tips on renting, see 'Travel Tips' on this web site, but don't be intimidated by all the detail; people often make renting a car seem more complicated than it is. Enjoy your trip!

The three places you list are easy to get to by train and in Munich itbwould be a negative and you can't drive in Rothenburg. My last 3 trips totalng 8 weeks were all done with train and bus/tram/subway. For long distance fast trains , get tickets online in advance. You can get St. Goar to Rothenburg for 120E for all 4 of you. book at www.bahn.com
For shorter trips, there are daily group tickets that you can get at the station - no advantage in getting early

Use this webpage (https://reiseauskunft.bahn.de//bin/query.exe/en) for Bahn schedules and fares. Bahn.com or Bahn.de will link you to this page; might as well start here.

Your destination, Rothenburg ob der Tauber, is not spelled "Rothenberg". Correct spelling might help you get where you actually want to go.

I've compared the cost of public transportation with a rental car before most of my 11 trips to since 2000, and I've always found I woukd save money by not renting a car. My trips have always been for one or two people, so, for comparison, I've picked the smallest car (compact) that I would feel comfortable driving on the Autobahn.

For four people and their luggage you will need a bigger, more expensive car than for two. Regional passes for four people cost less than 50% more than for two.

"Tentative itinerary is Frankfurt (flying into), St. Goar, Rothenberg, Munich"

Some tips for St. Goar and the Rhine...

Trains are great in Germany, including the most scenic part of the Middle Rhine Valley (St. Goar etc.) Train tracks follow both the east (right side) and west (left side) riverbanks and meet up in Koblenz at the northern end. Express trains connect the main towns, local trains stop everywhere. Here is a schematic train line map for that scenic zone; see the dark green line (RB10) for the east bank train stops, the light green line (RB26) for the west bank stops:

http://www.der-takt.de/fileadmin/_processed_/csm_Karte_3000_af861764b7.jpg

Once you are in St. Goar, you can do day trips from St. Goar using inexpensive day passes. A VRM "mini-group ticket" covers all of you for a day at a price of €23. Travel anywhere you like within the VRM zone (light green area.) VRM is the local transportation authority.

For day trips outside the VRM zone, use the Rheinland-Pfalz ticket day pass instead (€39/4 adults.) Travel anywhere within the larger R-P zone.

You can buy these day passes from a ticket machine on the day of travel for these prices. Very simple.

How do you get to St. Goar from FRA airport in the first place? If you look only at the DB website, you'll find a price of €82/4 adults for normal tickets on the regional trains. DB also sells day passes for weekdays (€68 for your group) or weekend days (€62.) But you can do better...

The price is only €51 if you buy two tickets... one to Bacharach (which is on your route) and another from Bacharach to St. Goar. Just go to a ticket machine at FRA's Regionalbahnhof station and buy one normal DB ticket for 4 adults between Bacharach and St. Goar (€16.40) AND one RMV group ticket (Gruppentageskarte 5 Personen, €34.50 at price category 6 for up to 5 adults) for FRA - Bacharach. (Note: Don't get off the train in Bacharach just because one ticket ends there - just have both tickets handy to present to train personnel.)

All the day passes and tickets mentioned above apply to the local and regional trains - be careful not to board any high-speed, long-distance trains (ICE, IC, EC, etc) at the airport or elsewhere.

St. Goar is a good Rhine base because of the ferry there, which runs all day long. Trains cannot cross the river between Koblenz and Wiesbaden, but the ferry landing across the river from St. Goar is within easy walking distance of the St. Goarshausen train station, should you wish to visit Marksburg in Braubach or the other east bank towns. See this St. Goarshausen town map. And you pay nothing for this ferry crossing if you have either the VRM or the Rheinland-Pfalz Ticket day pass in your hands - it's included.