I will answer your question in 5 years when I have added 5 more cruises to my list.
Currently I am not qualified to answer having only taken 2 cruises with both on the same line.
Although the Zuiderdam was better than the Amsterdam for all-round enjoyment.
Finally getting back on a Dam ship, Nieuw Amsterdam Nov'11 (My Mom's 80'th B'day cruise)
Navigator of the Seas 2010
Serenade of the Seas 2009, 2011
I should have gone into more detail like you did; my first cruise was on Island Princess; and there is just something about a first love. I don't know anything about Carnivale except it was/is a classically beautiful ship, as is I.P./Discovery. And to think, no balconies, not even in suites, no 24 hour buffet, tiny casino (two dozen slots), one dining room, two lounges, one small botique, no art auctions (horrors), no burgers, pizza or ice cream by the pool, tiny spa and gym.
It's hard to say which is my favorite, I love them all. My wife and I agree on the Voyager Class ships though. I also prefer to cruise on newer ship if I can. I'm looking forward to sailing on the Liberty in October.
Jill SC, Royal Princess is right near the top of my list. When I first sailed on her in 1986 the biggest ship I had been on was the 20,000 gt Island Princess so at 45,000 gt, Royal Princess seemed enormous; today we would refer to it as a small ship.
Her buffet was so big and she had so much deck space that it never felt crowded, even at peak times. I was very sorry to see her leave the fleet.