You can't even compare the two lines, so don't even try. Disney has the obvious "disney attention to perfection" and the over the top themeing. Carnival has over the top decor. Disney is all about the schedule, Carnival is all about the fun. They are both fabulous cruises, but both very different. Food is more gourmand for the adults and more kid friendly on Disney, On Carnival, its good, restaurant quality food, a little light on the kids side. Carnival's kid programs are more activity based, on Disney, they are more character based. Carnival has movies on its TVs and out on the deck, Disney has a special theater.
You can't compare apples to oranges, but in the end, they are both fruit.
Enjoy your cruise, enjoy the savings they are both wonderful values!