We chose the ship solely based on dates, length, itinerary, departure port. This ship was our only choice, we have friends who have sailed on Carnival (as had I in 1991) so off we went.
In fairness, before my comments below, fellow passengers looked to be having a great time. We had a great time. I have some positive remarks about the ship: great ship coffee! Great fitness center equipment. I liked this ship's layout -- it was easy to get around. And free soft-serve DIY.
We heard other complaints but that's of course not unusual for any cruise. Our other cruising -- about 20 cruises, have been on Princess mainly, Royal Caribbean and Celebrity. We've never had service nor a ship like this. Not even close.
We were not unhappy with the cabin size. A little cramped but no big deal. Balcony was fine.
Love Key West. We went to Truman Little White House and Hemingway House, plus Southernmost point for photo op. GREAT time.