We did a Danube river cruise on AMA a few months ago, and loved it. I’ve done a couple ocean cruises, and felt really trapped on the ship, surrounded by 2500 of my closest friends. But the river cruise was great, more like a floating hotel with no need to pack up in between locations. They had bikes on the boat, and we did some biking around towns. Excursions were included, and many of them were active and for biking or hiking. When we did take the city tour excursions (Vienna, Budapest), they divided us into groups, so there were only 10-15 people or so you were with. Also, for the most part, we were docked in town, and you could just walk into say, Vienna, in a few minutes, as opposed to an ocean cruises in which you could be stuck in some large port away from things.
Also, the boats together wasn’t a big deal at all. You just walk through a lobby of the other ship. That said, I did find it mildly irritating when I did a Nile river cruise a number of years ago. And the balcony cabin in Luxor had a view of someone else’s cabin in another boat for 2 days.