Wendy: Last year, we sailed on the AMA Armacello from Budapest to Amsterdam. Although the reverse itinerary seemed to be the most popular, the sail out from Budapest at night was spectacular and from our experience, couldn't have been better. It is completely different from ocean cruising but we loved it. They had three different groupings for tours which worked well for us as there was quite a bit of walking involved. If it had been up to me, I probably would have chosen Scenic as they had newer ships with a small balcony (as do Uniworld now), but the 'French' balcony was OK. I would definitely not choose a 'porthole' cabin but nor do I think the top level is necessary - we were fine in the middle but do try to avoid the cabins too near the rear as they can be a bit noisy.
With the space in which they had to work, it was incredible how they managed to serve the meals they did. Of course you had to turn up on time for meals, which is never a problem for me!
I have friends who have been on Avalon and Scenic and neither have any complaints but Scenic probably was more popular. I'm sure you'll enjoy whatever you choose.
Lee