Rasher, as you state opinions are personal and differ. FWIW I have done the route up and back from the Harz area and personally don't think you'll be disappointed. Not boring and the further north the better. Once you reach the Harz - for my money better than Black Forest. Roads are brilliant and much quieter than Black Forest and cops not as much a problem. You need some luck on your side regarding weather of course and if it's dry when you are there you will love the quality of the roads. Fast speeding bends with near perfect road surfaces. Lots of good routes but hard to find if you don't know the area. Suggest you might contact Peter at Hotel Harmonie and even if you're not staying there ask if he would give you a day tour. Fantastically capable biker who knows every road and every bend. Well worth a few quid for a tour around the area. Enjoy your trip.