There are a large number of companies serving the rivers throughout Europe. First you need to determine what you want to see. France, Germany, Eastern Europe, or any of the northern countries. France is very popular as are those in Eastern Europe. Next locate those who serve those areas. Next you need to determine if you want to be at the helm, more personal experience, or if you want a traditional cruise with a Captain and Crew. As far as the best that again is all in what you want. Viking is very popular and very expensive. The best times are not in the summer, too crowded! The prices are likewise higher during the tourist season. Fall or spring are great since it's less expensive and you can can find a better deal with all your travel. Hope that helps. If you have any additional question please let me know.