With kids? I vote Carnival too. Heck, they made me feel like a kid again! RCI was also a lot of fun and does have more goodies (rock climbing wall/ice skating etc etc) but Carnival was just more kid friendly.
Without kids? I vote for RCI. Much cleaner and relaxed.
Those are my two cents anyway!
Please make sure to watch the kids as I'm sure you will. We saw a little girl . . dripping wet and running around. She fell and there wasn't a parent in sight.