I have never used AAA but I shopped around for my April cruise and found a significant difference between prices on Travelocity and Expedia. We booked with Travelocity and everything was great. We added transfers later and got a new set of tickets. Saw no problem.
I understand that Carnival will honor any price, so if you book with Carnival and find the price cheaper elsewhere, they will drop you price . Correct me if I am wrong.