Well it depends, on what you want in your cruise experience, who you have with you, and what you expect from your vacation.
Carnival- Fun ships,
Princess and Holland America- Mid america feel, Good shows, okay food. <Lots to do.
Luxury -more all inclusive like Crystal,Seabourn, ect Food wonderful, interesting itineraries, more over night ports of call
Best of luck, and by the way USE a good Travel agent to help you.