This might help a bit:
From that list, although I havent been, I would choose Basel or Cluj N.
From that list Sibu or Salzburg
Finally if you start sort of close to Christmas and want to stretch it out, two cities not to be missed are Lviv and Kyiv. I say for a late start because Ukraine is orthodox and their Christmas is January 7th and their New Year the 14th. But their events are scheduled to overlap both Western and Eastern holiday dates.
Lviv is still a very cultural experience and a one off experience. https://hotel-edem.lviv.ua/en/christmas-in-lviv/ and https://www.youtube.com/watch?v=8mAbTBBZEhU
Kyiv and Basel are non-stop from Budapest for about $100.
Lviv requires changing planes someplace
Sibu and Cluj N. are best by train for connection in Bucharest.
Salzburg from Vienna
If it were me and my goal were Christmas celebrations, I would fly into Budapest, then on to Krakow on LOT (non-stop about $100), then on to Lviv on Ryanair (non-stop under $100), then home on Turkish Air through Istanbul to the States (Turkish Air is about my cheapest way to Europe).