I wouldn't place NCL at the bottom with Carnival. Mainly because you can't compare the two. Norwegian offers a lot more on their ships than Carnival. And for everyone who criticized Freestyle Cruising, many seem to be copying it in one form or another. We have sailed Carnival, Princess, Holland America, Norwegian,Royal Caribbean, and Celebrity. If I were going to compare lines, I would compare Royal Caribbean to Carnival, except for the fact they are more expensive. Both lines are geared towards families and fun. Royal offers more on board, and much bigger ships. Whether or not that's a good thing .........
Compare Princess to Celebrity. We loved them both, and did B2Bs on both. Both are for a more experienced cruiser.
Holland America is amazing! Great food, great service......but........a bit of an older,more sedate crowd. Not a party ship by any means. But, you make your own good time.
Norwegian, takes a little getting used to. But we love them. Food choices are excellent. Service is great. Customer service is amazing, possibly better than HAL.
It depends what you are looking for. Want to party? Carnival or Royal are your best bets. Going to ALASKA? HAL or Princess have smaller ships perfect for going where others can't. Want to get away as cheaply as possible ? Carnival. but, you get what you pay for.
Hope this helped a little. Enjoy whichever line you choose. It's still a cruise, and it beats being at work.
btw, we leave from NY almost all the time now, so we like the fact Norwegian is here year round.