I have done river cruises but not in Europe. Did a Med Cruise last year. The Med cruise allows you to travel farther, with activities on board at night. We spent extra nights before (Venice) and after (Barcelona) which gave time to explore those cities on our own. Some cities, like Rome and Florence are not close to the port so you spend a lot of time just getting to the cities from the ship.

River cruises tend to get you really close to town, so you do not spend a lot of time in transit. And the tours are often include in the price. But the activities at night or even the gym are minimal.

Part of the decision is where you want to go. I always wanted to see the Acropolis of Athens and Dubrovnik, Croatia. It was easy from the Med cruise, but not on a river cruise. Just got a tease of Rome, so we have to go back.

Traveling down the Mekong, can only be done on a river cruise.