My wife and I sailed on the Viking Romantic Danube cruise April/May 2018. We did the pre-cruise excursion in Budapest and the post-cruise excursion in Prague. It was mostly good, but with a few issues. Here are the pros and cons:
Pros:
1. Friendly and attentive staff.
Cabin was small but very well appointed, clean and comfortable. Steward service was unobtrusive and excellent. Storage space was more than adequate. Although the verandah was small (you basically have to sit sideways), we used it fairly often.