We've done a few cruises.
Norwegian Cruise Line (NCL): Our honeymoon was a 21 day Trans-Atlantic cruise from Miami to Barcelona, then a separate jaunt to Ireland. The cruise was on NCL - we upgraded our Penthouse cabin so that it included a Butler and Concierge service, and it was wonderful. It was off season, so it was dirt cheap compared to a normal trip of that scale. The food was to die for.
Royal Caribbean Cruise Line (RCCL): a 7-day cruise to the Eastern Caribbean. Nice accommodations - again, I upgraded to a private balcony room, and I loved that aspect of it. I had an awesome time, mostly because I traveled with a large group, and they are a blast.
Norwegian Cruise Line (NCL): a 7-day cruise to the Western Caribbean. Great accommodations and terrific food. This time we used the ships' Kids Corner for their activities and babysitting service. Great trip, but I didn't enjoy the Western Caribbean too much. Poverty and danger seemed to be the prevalent theme there. Returning customers to a cruise line get some awesome benefits/upgrades.
Carnival: I am booked for a 5-day Western Caribbean cruise next month with my sisters. I love the idea of going on vacation with my sisters, but I have no real interest in returning to the western Caribbean. I'll just end up hanging out with them instead of doing any exploring.