We just booked the Nautica from Istanbul to Venice, after doing the apples-apples comparison to the Navigator and deciding the cost would be about the same, but the itinerary was longer and included several ports I wanted to visit, like Montenegro and Amalfi. After two Radisson cruises, I expect the nickle-dime aspect will drive me crazy - I love the attendant bringing me a Diet Coke when I enter the room - all over the ship. I'm not much of a drinker, but I am a foodie, so the cuisine reviews were critical. I understand there are problems with Oceania excursions, so may try to do without them.
I was on a Renaissance cruise, so I know the boat, and have no serious problems with the smaller cabin - my wife is sacrificing her tub. Itinerary is just too major an issue.
David