By the way - the OP is correct about Carnival singles supplements - but they are only offered for the Fantasy-class ships (except I did see one exception for "Valor" a newer ship).
Quantum of the Seas also has some discounts for singles - including no singles supplements. I would opt for that ship (although it does cost more, it is much more interesting).
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.