I've been on Carnival and RCI a couple of times each. My favorite . . hands down is RCI.
Carnival - lots of screaming children and adults. Pool side was always littered with dishes and glasses full of cig butts (I was a smoker at the time but would NEVER put it out in a drinking glass). 3 year old kids dripping wet running in the halls and the elevators.
RCI - seemed to be a classier group of people. The kids cruising the halls and in the elevators seemed to be dry and more polite.
Yes, I would cruise Carnival again but would prefer RCI.
I've never had a bad cruise . . just have my favorites!