We chose Emerald based on the excellent cruise of the Moselle and Rhine 3 years ago. We booked the Duoro and chose the cabin and stuck with the booking throughout covid problems and are so glad we did.
The relaxed nature of River cruising is perfect and to mix with people who are mostly f the same age makes for a comfortable atmosphere.
The Douro cruise is at a much slower pace than some rivers yet has the right balance of sailing (daytime) only and excursions.
Marginally tight with a large double bed to gain easy access to the bathroom, other wise clean and modern with plenty of storage space.