We had heard that Carnival was not as good as Royal Caribbean but we decided to try it. Our last cruise was on Carnival and we had the best time yet. I think it depends ship by ship. My thoughts, Royal Caribbean is a bit more elegant but they were newer ships so a newer Carnival might be the same.
I don't know if this makes sense but we felt we were valued on Carnival not one of the huge crowd like we had been on Royal Caribbean.