rent a car or train

For four people, you'd do fine to rent a car cost wise. Just make sure everyone travels light.
The region is easily driven, so you should have no problems.
I like Bavaria Ben's websites for tourist info in the area. We've stayed a couple of times in Bacharach, a small city on the Rhine south of Koblenz.
See http://www.bensbauernhof.com

If you are going to rent a car, make sure there is enough room in the trunk for everyone's luggage. Leaving a suitcase on the seat is an invitation for thieves.

"Does anyone know how much a 8 day train ticket would be for 4 people?"

Your best deal is probably a German Rail Pass. They do sell multi-day passes. They come in 7 or 10 day versions, no 8 day. I imagine you could find at least one of your eight days where tickets would be a better deal, so you could get a 7 day (or fewer) pass. Rick sells German Rail passes here. The price depends on the age of the teenagers.

But do look at the price of just tickets. Use the Bahn website. If either of your teenagers are under 15, they travel free with you on full fare and discounted tickets. Standard (full) fare tickets are fully flexible (ie, usable on any train within the validity period and can be purchased at any time. Savings fare tickets can be deeply discounted if purchase far enough in advance (3-92 days) but usable on only one train and non-refundable. A good deal if you can commit in advance.

You can also get regional passes, good for unlimited travel for an entire day (after 9AM workdays). One of these would be valid for everyone in your party. Some are valid for only one German Land (state); others are valid for all of Germany.

I last used a rail pass in 2000. After I came home, I went over the trains I had ridden and what tickets would have cost, and I concluded that I just barely broke even, but if not for the pass, I might have chosen a few different trains and spent less with just tickets. Since that time (9 trips), I have always planned my travel in advance and compared what I expected to spend with a rail pass, and a rail pass never made sense cost wise. I also check the cost of renting a car (for just me or for two people) and a car never comes close to being cost effective. And I compare it to the cost of the smallest car, which would not be suitable for four people.

"I am going to be traveling with my Mom and two teenage daughters for 8-9 days, mostly the Rhine valley and as far South as Nurenburg."

These areas are well served by train and by cheap passes. Let's say you're traveling every day and using group daypasses. Here's the cost of a hypothetical trip for 4 passengers for eight days:

Day 1: FRA to Mainz for one day/night: RMV Group ticket, €15
Day 2: Travel to Boppard for 4 nights. Do a daytrip somewhere - maybe take a cruise from Oberwesel to Braubach for Marksburg Castle. Use the train to get to and back from your cruise points. Rheinland-Pfalz Ticket daypass, €35
Day 3-5: Day trips to other towns and villages (St. Goar, Oberwesel, Cochem on the Mosel, Moselkern/Burg Eltz, Remagen.) 3-day VRM pass, €43.60
Day 6: Boppard - Nuremberg, €68 for a QDL ticket/daypass (only €44 on Sat or Sun.)
Day 7-8: Daytrips to Rothenburg, Bad Windsheim, Bamberg: €35/2 days

That's just under €200 total tops, less if either teen is under 15.

I guess you need to get to an airport at the end on top of that too.

I vote for renting the train! Oh, that's not what you meant! ;-)

Do you have your itinerary worked out yet? It's hard to do an oranges-to-oranges comparison of car vs train without knowing exactly where you're planning on going - and how often you'll be 'going'.. A car might be more cost-effective, but more of a hassle, for instance, depending on your route. Also, a car could be a pain if the four of you are traveling with more than one piece of carry-on-sized luggage each.

Thanks for all the responses. I am thinking of spending 4 days at the Rhine/Mosel and Lanstuhl where I was stationed and my youngest was born, then 4 days in Nurnburg/Rothenburg/Dinklesbuhl/Nordlingen with possibly as north as Bamburg and west as Heidelburg. I was plannng on a car, but maybe a train would work.
Russ thanks for the price breakdown, 200 euros sounds like a great price. How do you find the prices and can I book them on line? Are you in Paradise, CA?

Why did my response come out like that??

You can verify the ticket types and prices as follows:
Landstuhl - Boppard (or St. Goar, Oberwesel): Rheinland-Pfalz Ticket
3 days of daytrips by train from Boppard: 3-day VRM Mini-group ticket
Boppard - Nuremberg: Quer durchs Land Ticket or Weekend Ticket (for Sat or Sun)
Nuremberg daytrips to Rothenburg, Nördlingen, Dinkelsbühl: Tagesticket Plus
(Note that Nuremberg is a weak travel base for these destinations and your trips will be quite lengthy - almost 2 hours each way in some cases. Ansbach as a travel base would shorten most of them. The Tagesticket Plus can be used from Ansbach as well. I would also say that your 3 chosen towns (R'burg, Nördlingen, Dinkelsbühl) are somewhat similar to each other - and NOT the only worthwhile destinations. Bamberg is wonderful (and a much shorter trip by direct train from Nuremberg.) So is the walled wine town of Iphofen (45 min. from N'berg.) Bad Windsheim is also less than one hour from Nuremberg - fantastic Freilandmuseum or "open-land" museum there.

Iphofen photos
Bad Windsheim's Freilandmuseum

Itineraries: To find connections on the eligible trains for all of these trips, you need to specify "only local transport" under "means of transport" at the DB itinerary page. These local/regional trains aren't luxurious but are clean and comfortable enough.

MRB trains on the Rhine
Double-decker trains
Double-decker upstairs seating

Although some daypasses CAN be purchased in advance, there is zero advantage to buying before you go - seats cannot be reserved on these local/regional trains anyway; passes never sell out, and you just buy them at the station in Germany at machines that will resemble these two in Boppard. It is in fact a handicap if you have pre-bought tickets and want to change your plans because of weather, illness or whatever. For convenience, you can buy them the day before as you step off the train for your next day's journey if you are sure that you will be doing your trip as planned.

Yes, Paradise CA.
Happy planning.

Trains have one big advantage that Lee does not mention. If your mom or the teens get on your nerves, you can leave them together and move to another car. They can do the same if you misbehave. You cannot do that with an auto, and they know you will not follow through on threats to stop the car and put them out. :>)

If you do rent a car, I highly recommend to choose a station wagon. That would give you more room for your luggage. And they are very common in Germany.

"If your mom or the teens get on your nerves, you can leave them together and move to another car"

LOL, Roy! NOT that I have had any experience with that... 8-/

And it's well known that most women have one bladder, and most men have two...The toilets are easily located at the end of most rail cars...no detours necessary.

BTW, this is a wonderful opportunity for the four of you to get to travel together! (Remember - all four of you don't have to be attached at the hip; occasionally, you may want to split up to better serve your interests.) Have a fantastic trip!

Thanks again for all your replies. Russ thanks for your detailed thoughts and prices.
I live in Oroville!

When comparing prices, you need to add the cost of any additional insurance you may want, and of course gas and parking fees. Make sure the back seat of the car is big enough so the riders don't feel cramped. If Mom (probably the front seat passenger) isn't a good navigator . . .

Trains are so comfortable. . .

What else have you planned besides the Mittelrhein and Nürnberg? If your trip consists primarily just of these two areas, a car probably won't add anything, unless you plan to take extensive daytrips outside the Rhine valley from a base there.

Allow me to comment on one of those dreaded legendary travel monsters that you hear about often, but rarely experience (like the thief who slashes day bags open or the one who wants to steal your used digital camera)- parking. In Germany, it generally isn't a significant cost, nor that much of a problem finding parking space, with perhaps Munich being one exception. I can't remember the last time I stayed at a hotel in Germany (or Europe, for that matter) that didn't provide eitherfree on-site parking or an arrangement with a nearby garage. Parking is usually easy to find, because large blue and white signs always point you where to go, and in cities, will even inform you how many spots remain. And the cost generally isn't significant. At most, I think I've paid maybe €100 to keep my car at an airport lot for 10 days, and the highest daily rate I've ever paid was maybe between €15-20. Parking for a few hours is generally no more than €5, and usually much less.

Now the high cost of fuel... yes, that legend is all too true.

For the area you plan on visiting I would suggest renting a car. You can definitely explore these areas using public transportation, but you will probably end up seeing more by renting a car.

Traveling in the Rhine Valley requires stringing together a series of trains and buses to get you from town to town and up to the castles above the valley. Additionally there are many castles, palaces, and monasteries that do not have good connections to public transportation. Linking these destinations with a car allows you to drive directly from site to site and expands what you can see in a day. Castles and town all have ample (and often free) parking.

Also keep in mind that cheaper rail tickets in Germany only let you use slow trains which will eat into your valuable vacation time. A slow train between the Rhine and Rothenburg may take up to 6 hours with multiple connections. That’s a long day with two teenage daughters.

It’s up to you to determine what your priorities are concerning what you want to spend, what you want to see, and the pace of your travel.

I am generally a 'car 'person' but that is because I like to be on my own schedule, come and go as I please (not by a train schedule) and like to veer off the beaten path as much as possible. I agree with Tom about the parking... I think it is relatively cheap and well marked parking is everywhere. I love the flexibility of road side picnics and stopping whenever I want. I have traveled with 4 people and a midsize car with no problems...however, fairly light packers. Yes, gas is expensive, but the European cars certainly get better gas mileage. I find putting my stuff in the trunk of the car at the hotel to be so much easier than getting to the train station (it is rarely outside your hotel door) then lugging it around again once you land at your destination. There are often times taxis involved that you also must calculate in your costs. Either way I am sure you will have a great trip...what a memory for your family.

We were a family of 4 and rented a car (Opel) for 2 weeks. Space was good but we limit our luggage to 2 carry-on size pieces each. The advantage of renting is that you set your own time schedule and are not tied to train schedules which would have killed us with a teenager that did not want to get up in the morning. When we made room reservations I always checked if there was parking available. Twice we paid to park but it was about 10 euros per day. If you travel by train you have to log your luggage to and from the station, up and down stairs. I had a GPS I bought here that would tell us what was the speed limit. We even programmed our destinations before we left on our trip. Have fun!