Have you been on the Carnival Fascination? It is an older and smaller ship, but was filled up by the company sponsoring the event, not Carnival.
I haven't cruised with Carnival, but I once booked a spring break cruise on Carnival Destiny out of San Juan. A month or so later, RCI's Adventure of the Seas out of San Juan for the same dates dropped in price, so I changed to that ship. I was already familiar with RCI and decided to go with a known quantity. It was a wonderful cruise, and we had the best dining room servers of any ship I've been on.