For me, when taking a cruise (or staying at a luxury hotel) for the second time, it rarely equals or exceeds the first time. HOWEVER, Uniworld changed everything for me.
We cruised on the SS Antionette 2 years ago for the "Castles on the Rhine" and were impressed beyond our expectations.
This time we cruised on the SS Maria Theresa for the "Enchanting Danube" Budapest to Passau cruise. Not thinking it could possible happen, it did!
It's literally impossible to find anything to criticize. The ship, the Captain, the crew, the food, the bar, the itinerary EVERYTHING. Granted we stayed in a suite, but this was simply the most luxurious, comfortable and rewarding trip/cruise we've ever taken. We've done over 15 Sea or River cruises combined. Having a butler (or two) may be the greatest experience you can have.
For my money, if we want the BEST, stick with Uniworld.