We are planning a Xmas trip. We have 16 days. Days 1 thru 10 is a river cruise that ends in Budapest. My current plan is: Day 11 in Budapest (with cruise time that will be two full days); Day 12 - morning train to Salzburg; Day 14 morning train to Munich; Day16 - fly home. But now I'm thinking it might be better to take an extra day in Budapest, skip Salzburg this trip, and have an extra day in Munich too????? Does that sound like a better use of my time. I'm kind of worrried that on the Monday in Budapest - museums might not be open. And with it getting dark so early in Decmeber, the days will seem so much shorter. ALSO, New Year's eve is in Munich - any suggestions? My mother is 82 so a rave is out, unfortunately. Maybe an oompah band?
I can't imagine why you would want three full days in Budapest, particularly at the expense of missing Salzburg. Having visited both (in the interest of full disclosure I actually lived in Salzburg for five months), I think there is so much more to see and do in Salzburg than you will find in Budapest. If it were my choice, I would spend just the one day in Budapest (assuming that you have seen the highlights on Day 10), and spend two days in Salzburg.
We spent 3 days in Budapest right before Christmas and loved it. Check your dates to see if the Christmas markets are on. Make sure you go to the baths, Terror museum, synagogue, regular food market, etc. Days are short that time of year so you tend to cover a little less ground.