I would highly recommend the Avalon Waterways Cruise. We sailed the Danube and had a lovely time. The trip was packed with interesting sights. The Danube was lovely. The ship was small--there were about 122 passengers that one got to know if not by name then by sight.
The cruise director was enthusiastic and knowledgeable. The ship was very clean and well-maintained. The food was just average. The dining room was pleasant but noisy and the service a little slow so meals lasted a long time.
The passengers were all retirement age--mostly couples. Mostly American, with a large Texas contingent. Everyone was pleasant. We made friends with a few couples that we hope will last. Having educational seminars on board was an added bonus.
The excursions were well-done and they and the itinerary kept us quite busy. We did a lot of things.
The exercise room was small and there wasn't much in the way of entertainment but then I wasn't looking for that.