Advice Please! - Best Town for Base and Accommodations in Rhine Valley

With 7 nights you have time for the Mosel Valley as well as the Upper Middle Rhine Valley (between Koblenz and Bingen roughly.) A good Rhine base for you will be one of the Rhine towns closer to Koblenz... I would look at the west bank first.

Boppard, Rhens, and Spay should turn up lots of apartment options. A car allows you to look for apartments in the hinterlands or high on the cliffsides as well as within the riverfront towns themselves - you will find many nice private places (most are apartments, fewer are B&B's) at even better prices but of course you'll need to be willing to drive into town much of the time. Most apartments won't have a/c.

I stayed in Bacharach at the Hotel Malerwinkel which has on site Parking,nice hotel with included breakfast.I stayed on the Moselle at Bielstein in a great hotel, Hotel Gute -Quelle with a balcony and great included breakfast on the river by the boat pick up Point.
Mike

I like Bacharach but I would choose St Goar for your long stay. Bacharach is too small for 7 nights.

Because of its ferry crossing, St. Goar is better if you're traveling by train, as a rule, but I suspect you will be using the car that you mentioned mostly. St. Goar and Bacharach are about the same size - relatively small - 2,000 - 3,000 population. For a larger town with lots of eateries, accommodations choices, grocery and other stores - and a nice waterfront - Boppard (about 15,000) with its location near the mouth of the Mosel River is hard to beat, IMHO.

Some aerial photos may be helpful...

Boppard: https://www.fotocommunity.de/photo/boppard-am-rhein-robert-bauer/40344229

Bacharach: https://upload.wikimedia.org/wikipedia/commons/8/81/Bacharach_Luftbild_01.jpg

St. Goar: https://i.ytimg.com/vi/gaXwloCJwgI/maxresdefault.jpg

We used Bacharach. Very picturesque and everything is close.

I stayed in Bacharach but it was only for one night. For a longer stay I would choose Boppard. I loved what I saw of it when I visited for a short time and it seemed to have more to offer than Bacharach for a long stay.

I know you have a car, but some trips are still more relaxing than driving. St Goar and Boppard are in the VRM transit district with inexpensive day tickets for the district, which runs up the Mosel as far as Traben-Trarbach, down the Rhine as far as Rolandseck (outside of Bonn), up the river as far as Oberwesel, and as far east as Limburg. Bacharach is outside the district.

Thank You everyone for the input!
I'll take a look at Boppard. Of course, if anyone has a favorite accommodation in that area to recommend, it would be appreciated.
Is there any reason not to consider Koblenz for an extended stay? I haven't seen it recommended often...if at all.

Koblenz is alright but more than a little modern and by comparison less charming - only a very small bit of its older self survived the war. It's OK for getting a room in the winter when the smaller Rhine towns are mostly shuttered, but most visitors in the warmer months probably prefer the old-world charm of the other towns.

I've stayed at several different places in Boppard and St. Goar. But not all of them. So my judgment is particular to my experience and therefore suspect... Because individuals here have their different priorities - location, price, a/c, in-house restaurant, comfort level, etc.... I think you're best off using your own judgment and making a selection using the comments and ratings you will find on the booking engines and travel site pages (like booking.com and Tripadvisor) where there are hundreds of reviews and aggregated results.

On the Rhine I would stay in Bacharach, but not for that long. Maybe 3 nights at the most. Then I would move my home base to the Mosel. Cochem is a good choice there as you can visit the castle,(Burg Eltz) going one direction and my very favorite German village, Beilstein, the other direction. It's not far away, but on the other side of the Mosel River. I like to rent a bicycle and bike along the river, using the little ferry to cross to Beilstein. Probably my favorite thing to do in Germany.

We stayed at the Rhine Hotel Bacharach twice (and sent the in-laws there too for their anniversary). https://www.rhein-hotel-bacharach.de

Bacharach is small, but central if you have a car. Although Americans are used to having a car, and they are good for out of the way stops, we lived in Germany for three years without a car and only rented one several times.

I don’t think there is any problem staying for a week in Bacharach.

i’ve stayed for 5 and 7 days in the past and have another 7 days scheduled.

Train connections to Bacharach are easy. You can get a train from the Frankfurt airport if you are flying into there. It only has one change. I believe Bingen is a bit larger than Bacharach, if that's what you are looking for. Bacharach is always my first stop when I travel to Europe. Others I have taken there find it charming as well.