We are just starting to plan a trip arriving in Frankfurt and have one week to get to Zurich. We prefer smaller towns, lovely countryside, and hikes. I know this is very general, do you have any suggestions for "must-see" places along the way? Lovely towns? Thanks.
I'll just point out one - Lindau on the Bodensee. Beautiful town and lakefront.
Are you driving or taking trains?
By rail, any number of sights along the way. Since you start in Frankfurt, spend a day to take a cruise on the Rhine from Ruedesheim to St Goar to see the best part of the Rhine Gorge. Then you could head south and take a slight detour to Strasburg, France,. then train to Gengenbach at the start of the Black Forest. Then continue on the rail line to Triberg (Cuckoo Clock central) for hiking in the Black Forest. Follow the rail line to Singen, then you are a short train ride to Zurich.
Lindau is a great stop, so is Strasbourg. Other towns worth considering are Freiburg, Colmar, Baden-Baden, Konstanz and Ludwigsburg.
I agree about St. Goar in Germany and would add the nearby town of Bacharach, both in the lovely Mosel area. They're cute, walkable towns and are even better if you like wine. Some wine shops might even have free tastings.
For your last stop before Zurich, you might want to go to Luzern (Lucerne), Switzerland. It's about 45 minutes by either car or train to Zurich. I've never been but will be going there in early September on my own Germany/Switzerland trip. Luzern looks beautiful, has surrounding water, and is close to both Mount Pilatus and Mount Rigi to which you can take a cable car/cogwheel train and go hiking.
Good luck planning and have fun on your trip!