I've been on the Disney Magic too many times to count, and my family was on the Carnival Magic (out of Galveston) just this past summer.
First off, I would choose which ship by itinerary. I wouldn't like the
DCL trip going to Key West,
Castaway Cay, Freeport or Nassau, because I could take(and have taken) that cruise out of any port in Florida....and other than Castaway Cay, they aren't anything special.
We went to Jamaica, Grand Cayman and Cozumel on Carnival, and I loved the ports...much more worth the time and money than the alternatives.
The cost of the Carnival cruise was cheaper than a comparable
Disney cruise.
I happen to like the choices for the main dining room menus BETTER on Carnival. They have the "specials" that change daily (several of them) but they also always have one side of the menu listed as "Comfort" foods, and healthy alternatives. Comfort foods like a big burger, fried chicken....and also more dessert choices, not to mention MANY more alternate restaurants than on Disney, and those that do have an upsell charge are minimal, less than Disney, and family-friendly.
Our cruise on the Carnival Magic was fully booked, but didn't feel any more crowded than any other cruise I've been on. A fully booked ship is going to have a lot of people, whether it's a small ship or a larger one.
I loved, loved, loved the extra hot tubs that were outside along the Promenade Deck. While the regular pool areas might have been crowded, these (not too hot) hot tubs seldom were.
LOVED the Red Frog Pub, and the multitude of different activities for families and adults all day long, like the trivia-type games.
Don't get me wrong, the Magic and Wonder (Disney) are awesome ships, and I much prefer them to Disney's newer ships.....but I was REALLY impressed with Carnival's Magic. LOVED the cruise director, Gary.
We did NOT like the "adult" comedy after the first time we went, so from then on, we went to the "family" show comedy, and really enjoyed it. The family ones were funny and clean, whereas honestly, the adult ones were even too vulgar for my husband and 19yr old son.
But again, for the price, the ports and a lot of other plusses, the Carnival Magic was great.
I have pictures here:
http://smg.photobucket.com/albums/v444/justmestace/Carnival Magic 2012/