Bbgrizzle,
We've been on a few cruises, but not nearly as many as some others had on this board. Here are my opinions on the cruise lines we've traveled with before.
Carnival: Great for singles, young couples without kids, and families with older child(ren) (teen or older). Marginal for families with young kids.
Although they are trying to move away from their previous tagline of a "party ship" toward a more family orientation, their primary market is still the younger set. I mean, if you want to cruise and you're a single or without kids, Carnival would still be your first pick.
Princess: Great for older couples and mature adults. Ok for young couples and families with older child(ren). Marginal for singles and families with young kids.
Princess tend to attract a more mature audience and fewer families with young kids. The programs they offer onboard are mostly geared toward adults.
DCL: Great for families with young kids and any-aged Disneyholics. Ok for families with older child(ren) (teen or older). Marginal for singles and older couples (except for Disneyholics).
In my opinion, DCL is ideal for families with younger kids (teens or younger). Although other cruise lines offer "kids programs", they usually feel like afterthoughts -- mere attempts -- whereas the DCL's ships were designed with kids in mind.
Another huge differentiator of DCL is the lack of onboard casino. All other mainstream cruise ships have onboard casinos that take up large amounts of floor space. Meanwhile, DCL dedicates those floor spaces to kids activity centers instead. Casinos generate a lot of profit for cruiselines and they helped to keep the cruise prices down. This is partially why DCL cruisers pay a premium in price.