I think either would be a good choice. Pay more attention to the age and size of ship along with the itinerary. At 21 you'll find the newer larger ships have more to do and fewer small children than the older, smaller ships doing short sailings. If you choose RCI, look at Voyager Class or Freedom Class if the budget allows. On CCL the Conquest Class or newer would be a nice choise. You'll love your honeymoon cruise on either BTW, congratulations!
We are planning a 7 day cruise, eastern caribbean. I have heard that RCL is a bit more on the upscale side, but I have also read that it is an older crowd and there might not be as many activities geared towards the young adults. Anyone who has been on both that can give pros/cons of each?
Caribbean cruises on RCI and Carnival tend to draw from a similar age demographic. So, as long as you go with the suggestion of one of the larger, newer ships - there will be plenty of age appropriate activities and fellow guests of your age onboard both. Depending on the date of your honeymoon, if you travel during school vacations/holidays - be prepared for a large number of children and families on both.
All I can do is add my dos centavos to what Nancy and Neil have said.
1. There is no difference in the passenger ages between RCI and Carnival. Ages are more dependent on the length of the a cruise than on the line. Older people have more time to cruise. 7-day cruises on both RCI and Carnival attract the full range - babies to grandparents. It isn't worth worrying about.
2. Carnival and RCI are more alike than dissimilar. Food between the two is really the same in quality and variety. And it is very good too. Cabins are generally the same, although RCI has a slight edge in attractiveness of the cabins. Carnival has the edge in standard cabin size. The big differences come with the ships. RCI has the big lead when it comes to innovation and things to do on the ship. Nothing Carnival has can compare to the Voyager and Freedom class ships of RCI. Ice rinks, rock-climbing walls, flow riders on the Freedom class, the huge promenades, etc. Carnival has nothing to compete with it. What Carnival does have - in most but not all cases - is better prices. And that can be a big decision-maker for many people.
Itineraries are important. I loved the Liberty Of The Seas but the itinerary for the eastern run isn't my favorite. However, RCI makes good use of their private "islands" of Coco Cay and Labadee (really a small peninsula of Haiti). Carnival doesn't have them as a routine thing, although their ships sometimes stop at private islands owned by subsidiary cruise lines.
Set a price and then do some comparisons. If it were me I'd go for wow factor and the Freedom or Liberty of the Seas ships of RCI. But Carnival is not to be dismissed. Less wow factor but great service and a fun cruise. I've never been disappointed by either RCI or Carnival. And there are activities for people your age in abundance on either cruise line.
I've only been on Voyager of the Seas our family ranged from 16-40. It seemed to me most people were mature couples- not old, but mature. It was a 7 day cruise to the Western Caribbean.There were very few "old people" and very few "kids".
I can't speak for the Carnival ships...but I have seen my dad's videos!!!! Way to many kids for my liking! I don't think it's so much the "ship" as it is the time of sailing and length of the cruise.
When is honeymoon?
The time of sailing is the thing. For a Caribbean cruise - regardless of itinerary - the typical RCI ship's passenger demographic will pretty much mirror that of the typical Carnival ship for the same time of year, and same number of days.
Less kids on both lines when school is in session, more kids on both lines in the summer. I think we had 800 or so kids (defined as 17 and under) on the Liberty two weeks ago. On a New Years cruise on the Carnival Legend 3 years ago there surprisingly weren't that many.
I'm going to differ with Dave's assessment just slightly. There ar times during peak season when Carnival will have many more children than RCI on similar itins and dates. The reason is the # of quad and triple cabins they make available is very different. RCI releases only a select # of these cabins. When the hit their self imposed limit they pull availibility to book them even if they have many, many more available on the ship. CCL will pretty much fill their ships any way possible. They have so many triple and quad cabins, they are the only line that even allows guarantee ststus for not only trips and quads, some of their ships will hold up to 5 pax, even in inside cabins.
I know that availability of these multi-pax cabins doesn't mean they'll all be children and some people travel with an adult and a child each in double cabins. Simply the way their processes work make family bookings more likely with CCL when peak season availability for family cabin is gone with everyone else. Both lines are very family friendly and draw a lot of children during peak season and a fair share off season.
Of course, I have no way of knowing the details of the bookings and the cutoffs. I am going from my perceptions as a frequent customer of both lines - in the summer mostly. If Carnival has more kids on a sailing, it isn't especially noticeable - and that is the bottom line.
I think one thing that was remarkable to me, and tncruiseman will hopefully bear this out, was on our Holiday cruise this past March they said we had something like 400 kids aboard. Yet you never would have known it. A tribute to the Camp Carnival staff on the Holiday, and perhaps just a little bit of credit to all those southern families aboard - who have done a good job with their kids.
Oh, and before I appear to be contradicting myself....the cruise on the Holiday was during spring break for most schools in Alabama and many other southeast states! Thus we had a passenger load of mostly young families and their kids.