We have done a lot of tours through Europe and this was down the bottom of the list. I definitely recommend Salzburg - it is beautiful and the lakes district on the drive is spectacular if brave enough, I would recommend hiring a car and driving so you can stop for the views. Our tour guide literally rushed us through Salzburg, to the point that by the time we caught up with her she had finished speaking and was moving on, so we couldn't really hear much. She also did not have the nicest manner - she was quite short and unhelpful when we asked questions. We didn't really feel Vienna was the kind of city which needed hop on/off either - there was little interesting information provided, the narration didn't seem to match the timing of the monuments at all, and their wifi didn't work on any of the buses. I would find a way to get to Salzburg for the day, but would skip the hop on/off and research myself ahead of time instead.