I would claim that your first CRUISE LINE will become your favorite since it becomes the standard you compare the rest to. But not necessarily the first ship. Since the Freedom was/is a relatively new ship, I can see it being your favorite, but as time goes by and the ships get more amenities and style updates, the older ships will fall from your "favorite" list.
The Carnival Fantasy was our first cruise and she was brand new (1 month old actually) when we sailed on her. At the time she was considered the biggest and best... now she is one of the smallest. I still remember the Fantasy but she is not my favorite.
Now I am sure there will be excepts to that rule (like Dave's HAL cruise not imprinting HAL as his favorite line) but I bet for most people the first cruise line becomes their gold standard....
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
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013