The loop through Switzerland, Lichtenstein, Austria, & Germany is also a good choice. I'm also a little biased since I live in the area. The route offers spectacular mountain scenery, safe and dedicated bike routes (i.e., very low traffic), and route signs making it almost impossible to get lost. Swiss trains permit bikes (for a nominal fee), so you'll always have an out if the trip becomes too much (shouldn't be an issue if the trip is supported by a tour company). It's also useful for getting up big hills that might not be your fancy. Good luck!