River cruising in Europe has become the fastest growing segment of the whole travel industry. There are 8 companies involved in catering to the English speaking market. Each company is building one or two new ships each year and trying to outdo each other in terms of what they offer for shore excursions, food and service, accommodations, etc. The end result is that the experience just gets better each year.
The design of new ships is greatly constrained by the environment in which they sail. River locks are built to handle a certain width ship and, believe me, the current ships are cruising through the locks with less than a foot to spare on either side. They are also constrained in terms of height. The bridges are fixed and only afford a certain amount of clearance. In fact big problems show up when the rivers are high - ships can't get under the bridges.
This all creates design problems for each company. Some want to add real balconies (most ships utilize French balconies - you can open the door but can't step out). If you add a real walk out balcony, you can't make the ship wider (because of the locks) so you have to take space away from the room. Passengers are now making the decision between a step out balcony vs. a smaller room.
Just like large ships on the ocean, companies stake out their target market. Some set their appeal to the masses and some focus on the luxury market and the majority lives between the two extremes.
All companies in the river cruising market could be considered all inclusive compared to your average ocean cruising ship. They include shore excursions, bottled water in the cabins, free wifi connections and unlimited beer and wine with meals. The river cruise companies that bill themselves as luxury all inclusive add included gratuities, open bar, premium free excursions (things that others might charge for), and free transfers.
A standard of comparison among ships is the size of their cabins. When the industry was just beginning to cater to English speakers (in the late 90's) cabins were about 125 sq ft. As they have built new ships cabin size has increased to 150, 170, or even 200 sq ft. All river boat cabins are outside - some with windows (lowest deck cabins - bottom of windows is about 3 feet above the water line) - some with French balconies (floor to ceiling sliding doors) - and a growing number (on newer ships) with actual balconies that you can walk out on).
AMA Waterways - one of the newer companies in the market with thirteen ships in Europe. While not billed as a luxury line, their ships, accommodations, food, amenities, and service are certainly comparable to the companies billed as luxury.
A-ROSA - all inclusive line with a luxury orientation. Actually a German company which has been operating in Europe for many years. They have recently devoted 2 of their ships to English speaking markets.
Avalon Waterways - a division of Globus, Avalon operates fifteen ships in Europe. Their fleet is very new and their cabins are larger than most. While they don't bill themselves as a luxury line, their standards of food, service and included amenities are close to the levels offered by those lines in the luxury space.
Scenic Tours - an Australian company that addresses the all inclusive luxury marketplace.
Tauck Tours - is a luxury tour operator that has recently entered the river marketplace with ships of their own (they have offered cruises for quite some time using other companies' ships). Their cruises are all inclusive and feature some of best shore excursions of any of the companies in Europe.
Uniworld - known as a boutique line with a luxury orientation, Uniworld has 14 ships in Europe. Their boutique orientation comes from their partnership with Red Carnation Hotels (upscale boutique hotels in Europe). The ship's decor is reminiscent of a nice bed and breakfast hotel.
Viking River Cruises - is the largest river cruise operator with 40 ships. They mostly address the mass market space emphasizing first time cruisers and 2 for 1 pricing. On many of their older ships, standard cabins are 125 sq ft. Their newer ships are 150 sq ft and up. While prices are very similar to AMA and Avalon food, service and amenities lag behind those middle of the road ships.