Have cruised previously with Uniworld in 2012 on the River Princess from Trier Germany to Prague...an excellent choice.
The River Ambassador is a beautiful ship also, but the cabins are a little bit smaller, although the bathrooms are a little bit larger.
The staff of the Ambassador is fantastic, from the front desk personnel to the dining room waitstaff to the staff in the lounge. They are very friendly and really made for a very enjoyable trip.
BMW factory tour is a must...very eye opening!