Choosing cruise-company really depends on what your are looking for.
Carnival is often a choise for younger people.
Please note; CCL's "Carnival Freedom" and RCCL's "Freedom Of The Seas" is two really dissimilar ships, so don't let their names making confusion.
Maybe checking out their website and reading some cruise-reviews at www.cruisereviews.com
will tell you a lot about the different ships and cruise-company's.
Good Luck Choosing