We took Uniworld's cruise down the Enchanting Danube from Passau to Budapest. It was our second trip with Uniworld, and it was great. The tours were super, and the ship was outstanding. Booked through AAA @ Sumter Landing, (Kathy J.) for both our tours, and were very happy with bookings. You can probably pay less, but I don't think you can do better. JMO
Google Uniworld for info on trips and ships.