The Victory is a bigger ship. The Conquest class is the biggest.
I have sailed on each class now.. The Celebration (which is the oldest "class" sailing currently in CCL's US fleet. The Fantasy (which is the Ecstasy's class) a Spirit class (Pride and Miracle(?)). You can go to CCL's website and run through the different ships. Its too hard to list all the differences, but there is a difference between the Spirit class ship layout and the Victory/Conquest layouts. Many to allow there to be more Oceanview/Balcony cabins for the Spirit class ship.
The reason we say the Fantasy class is a prefect size is that the Larger classes (Victory adn Conquest) carry a larger number of passengers which means longer lines for tendering and buffets. I felt that the Victory always seemed to have huge lines at the buffets, but the Conquest (which is bigger) had added additional buffet lines which fixed the line problem.
We also had problems tendering on the Victory, but that may have been more due to Hurricane re-routing causing 7 large cruise ships all showing up in Grand Caymen on the same day. This made the GC supplied tenders well over burdened, so it took forever to get off and on the ship. We returned to GC on the Conquest which is even larger on a "normal" day and did have any problem at all.
If you go on multpile cruises, and try the different ship sizes, you'll "hit your sweet spot" on what you like. The Fantasy was our first cruise, so we are partial to that size ship. (They just seem to be running the shorter cruises and therefore we have not sailed on them since.)
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013