I sailed on the Mozart from Passau, Germany to Budapest via Vienna and back to Passau.
The Mozart is a 5 star riverboat, with fabulous food and excellent service.
Cabins are large and nicely appointed, and the crew speaks English, as well as German.
The majority of passengers were German, but about 1/3 of the guests were English speaking.
The various excursions along the way, were either with a German speaking tour guide or an English speaking escort.
They offered wonderful entertainment at night, mostly local groups in Vienna and Budapest.
It's a delightful way to see the small villages in tthe area and enjoy the flavor of the region you sail.
I'm not familiar with the Deutschland, and upscale Ocean Liner, who is also in the Peter Deilmann fleet.
I highly recommend Peter Deilmann, as they deliver an outstanding product.