Go to Cruise Critic dot com and post on both the Disney boards and the Carnival boards. You will get people obsessed with cruising answering your questions. Also, maybe you should consider narrowing your question down because there is no "good or bad" situation with these lines. It's all personal preference. Some people adore Disney and the characters and others find the ships packed with whiny 3 year olds and are looking for more balanced travelers (ie not everyone with a toddler). I would suggest you look through the CC boards and read some of the reviews on the ships you are interested in also. Many cruise lines have newer/larger ships and older/smaller ones and it's personal preference on which you'd enjoy more. Also, your destination matters.
I've cruise both lines (Disney coming up again in 2 weeks and Carnival Splendor in 3 months) and I know our family enjoys both, but for VERY different reasons. You need to do some research to really understand what you are looking for!
Katherine