I'm a RCI frequent cruiser, just tried Carnival last week.
If you are interested in sailing from Port Canaveral, try the Freedom of the Seas. It just moved to Port Canaveral from Miami this month and is doing Eastern Carib. itineraries that include St. Thomas and St Maarten. The ship also stops at CocoCay, RCI"s private Bahamas island. I must say, this island is by FAR my favorite port! It's perfect for just relaxing..either in a hammock facing the ocean or a lounger. THere are also plenty of adventure excursions available. I've sailed the FotS a few times and love her. Beautiful ship, wonderful food, exceptional service. The shows were very good also. The ice show is fantastic.
I have heard so many good things about the food on Carnival, and I must say, the food on the Imagination was AWFUL. We're not really very picky eaters, but the only thing any of us ate for 4 days was pizza and burgers and ice cream. Oh, and the chocolate melting cake. The dining room was terrible the 2 nights we tried it and the buffet dinner was not any better. I won't make a fleetwide assumption based on one ship, but I can't vote Carnival on this one!
The cabins on the Freedom of the Seas were similar in size to the OV we had on Carnival, if not a little larger. But be warned, the bathrooms are miniscule on standard cabins! Suite bathrooms are good sized, though.
Hope this helps!