Planning to travel with husband and three teenage boys from Frankfurt to Zurich next summer. I anticipate the trip will be about 9 days and it's our last big vacation before the college tuition years start. Since our "bookend" cities are large, and will probably require a certain amount of sightseeing, I was hoping to find two smaller places to stop en route and just soak up some ambiance. To get a feel for what we like, we have done trips to France and Italy and our boys liked Amboise and Bayeux - walkable, "authentic", Rick Steves kind of places! Our preference is to train, but a car isn't out of the question. Thanks!
(Not sure what "authentic" is supposed to mean, especially because "Rick Steves places" tend to be filled with souvenir shops... but anyways...) You have a choice of two routes to take you from Frankfurt to Zurich. One goes along the upper Rhine valley, parallel to the Black Forest and through Basel. The other would run through Stuttgart, Swabia and the Allgäu region. I would recommend the second option. Your direct line of travel would have you passing by the Bodensee. At an absolute minimum, I would recommend at least a quick stop-over at one of the lake towns, particularly Lindau. Whether or not to spend the night would depend on what else you had planned. If you're looking for some good Alpine hiking near Zurich, my favorite resort town in the area is Flumserberg. Good infrastructure for visitors (hotels, restaurants, ski lifts etc) but not completely saturated with the tourist trade.
On the Swiss side and coming from Germany, I like Basel (many museums, medieval Spalentor and town hall), Stein-Am-Rhein (Sometimes described as a "Swiss Rothenburg"), Schaffhausen, and the Rhine Falls.
That area of Switzerland is not covered in the RS guidebook but many other resources are available.
Gengenbach and Colmar or Riquiwihr.
Suggest you stay in Strasbourg a few nights, down to Riquewihr or Colmar for a few nights, then around to Meersberg Lindau before heading on to Zurich. Book hotels in those areas early, they tend to book quickly in summer.
As Tom suggested, the Allgau region is beautiful. Lots of hiking possibilities. On the way there, you could stop at the Hohenzollern castle south of Stuttgart. Then, from the Allgau region, I would stay in and around Lermoos, Austria. Lots more hiking, cable car up to the Zugspitze, Sommerolderbahns (summer luges for the boyssuch a thrill), and maybe a side trip to Innsbruck. Then head west from there towards Zurich. You could stop in Appenzell and see the cheese factory or do some more hiking. Yes, do your trip now before the boys get busy with other activities. These memories will last a lifetime. By the way, I would drive. Just my opinion and preference.
If you do go down Stuttgart way, let me bring up that both Porsche and Mercedes-Benz are headquartered here, and both have excellent museums in town to visit. Something boys of all ages tend to enjoy. On the Bodensee Freidrichshafen has the Zepplin museum which is also a big hit with people interested in crazy transport.