If you're set on Port Canaveral so that you can spend some time at WDW, then you're probably looking to book on the Fantasy. Although the Magic also has some 7-night sailings before it heads back to Europe for the summer. (The Magic's Southern itinerary includes Tortola; the Western itinerary includes Key West.)
The Fantasy has more "bells and whistles" technologically, but the Magic is classic. You can't go wrong with either one. I was just on the Magic for 11 nights this past summer and it was in great condition. If you choose the Fantasy instead, you'll love it as well.
If you really don't care where you go, then my suggestion would simply be to agree on a range of dates with your friend that work for both of you and pick the sailing that is closest to your budget. And do it sooner, rather than later; because DCL prices only go UP, never down.