If you are a first time cruiser and don't know which particular line you'd like to sail, find a good TA that can tell you about each cruiseline.
Even though I do most of the online work myself, I continue to use my TA. One, because we have become friends; two because she tends to find special deals that I haven't heard about; and three because it may just be coincidence, but everytime I have sailed I have been upgraded (I usually book a guarantee) - once from a 6A oceanveiw to an 8B balcony.
Carnival Elation March 11
Carnival Imagination Sept 07
Carniival Sensation Dec 06
RCI Sovereign of the Seas Sept 06
Carnival Miracle Sept 05
Carnival Glory Sept 04
Carnival Fantasy Jan 04