What are favorite (or recommended river boat cruise lines. Thinking of Vienna to perhaps Budapest or elsewhere.
You’d be better asking this in the cruise forum though I doubt you can do a cruise as short as Vienna to Budapest
Another question is whether it is worth doing that, considering the rather short distance between these two cities, but that's up to the beholder.
As far as I know, Austria's DDSG used to offer such short cruises from Vienna to Budapest, completed in one day though, if I remember correctly.