The Spirit class of ships is a series of four ships that Carnival built starting in 2001. The series of ships are identical in size and floor plans. They differ in their theme and decor. The first ship built of this series was the Carnival Spirit-thus the Spirit class. The Spirit was followed by the Carnival Pride, Carnival Legend, and Carnival Miracle. Which are then called sister ships. Occassionally you will see sisters ships with a slight variance like the Carnival Destiny, Carnival Triumph, and Carnival Victory. They are the Destiny class, but the Destiny has one deck less than it's sister ships. All cruise lines have class names to a series of ships built with the same design.
Spirit Class are probably my favorite of all the Carnival ships. I have sailed them all and try to book them any time I sail. The Spirit and the Pride are my favorites. Beautifully decorated with great food and service. Give 'em a try. You'll see.
We've been on the Pride and Legend and they were great. Frankly I preferred them very much over the Destiny class, which seem to have cluttered layouts and poor passenger flow on the pool deck - at least to me.
The other feature of the Spirit Class, they are the largest cruise ships that can fit through the Panama Canal, Carnival has 4 , Costa has the Atlantica and Mediterannia(almost exact carbon copies), and Holland America has 4 ships that are of a very similar design. .
I think that the guy designing the interior of the Miracle must have been on an acid trip. As a guy I don't really notice interior design but good lord that ship is ugly inside. The dinning room is the worst. I read reviews about it before we sailed but it is truly aweful. I had a great time nonetheless. Eyes became numb after a day.