Personally, from the top, I would select;
There's also one that has caught my attention - they just opened up their cruises to the No. American market - Arosa. We checked out one of their boats when were were on our river cruise and were impressed with it. While we've not sailed on them, clients we have who spent time on them were impressed.
Tauck & Scenic Tours are the best, but they're also luxury class, so alot more expensive than the others.
We're hooked on river cruises and can't wait to go again - truly a wonderful way to visit cities on the rivers that you can't get to on an ocean cruise.