We did RCCL this past July to Alaska. Our DD (10) says she prefers DCL to RCCL, but not by as great a margin as I expected. Cons to RCCL: hours are limited, with very little, if anything, to do in the kid's clubs between 4-8 in the evening. After 10 pm, there is a $5 per hour charge. There aren't very many unstructured free play items on board (there is the arcade, which is just outside the club). I felt the counselors were enthusiastic about there job, there just weren't very many of them--there were 112 kids under 13 on board, and 8 counselors total. DD and other girls her age group had a problem with a boy in the group who would deliberately hit the girls with a ball during free time--I asked the counselors to keep an eye on the situation, but she continued to be hit until the 6th night, when she and all the other girls ganged up on him and "retaliated".
PROS: because of the small # of kids, DD found it easier to make friends than on DCL (I don't think this would be a factor on caribbean cruises tho). I have read on cruisecritic that RCCL sometimes closes the kids programs because they have too many kids, not enough counselors. DD enjoyed the rewards program where you get credits for attending kids programs and can redeem the credits for prizes like bookbags, caps, t-shirts, etc.