I had only one cruise with Carnival in 2010. There are so many young people aboard, and you always could meet interesting one. Tha entertainment is also nice. But the ships are too big for my taste, I like smaller. But kids will sure enjoy the vacations aboard Carnival ships. By the way, I celebrated my B-Day on the cruise, and it was awesome! I got a huge chocolate cake (for example, HAL's cakes are 4 times smaller) and it was very delicious!
I had 9 cruises with Holland America Line and I really enjoyed each of them. Most of all I like small ships like ms Veendam or ms Amsterdam, because after a few days you could know most of the passangers and crew. My the most amazinf cruise was around South America with celebrating of New Year's Eve in Antarctica. The food is always nice and delicious, the only thing that I missed is a fresh orange juice (now they onle served the juice from the boxes). I love HAL unique itinerary, and the possibility to visit very special places on the Earth. I'm a 3 star mariner and got the bronze medal as well.