We've sailed all three and like others have said, we've found more similarities than differences. Ship is the biggest difference. We loved the NCL Getaway, weren't so fond of the Dawn and it's layout. Carnival Legend wasn't my favourite ship, and I really wasn't a fan of the food, but we're going on Magic this summer so there was more good than bad. My kids favourite was RCI, but they've loved the other ones. The only kids club either would go to was on Disney, so I can't comment on those. We try to balance cost vs ship vs itinerary. I have no desire to go on an older, smaller carnival ship but have no problem considering the newer bigger ones. Decide what's the most important features to you, and look for that rather than focusing on which line is my advice.