I agree with Trip!
First, and definitely foremost, book with a reputable agent and not with the cruise line! An agent will be able to answer ALL you questions and let you know what to do, how to do it, and where to do it. A cruise line represents themselves and should you have any problems, who do you think they will represent?
A good agent will be able to give you all the options and give you all the information necessary so you can make an informed decision, because as Trip said, comparing these two ships is like comparing apples and oranges - they really are completely different.