We haven't sailed on the Dream, but we just got back from a trp on the Fantasy last month. We cruised last year on the Magic with an almost identical itinerary. We loved both trips, and each boat has its pros and cons.
We found the food and the service to be better on the Magic. The service overall was still great on the Fantasy, and all the CMs were great, but dinner service in the MDRs and the quality of the food was better on the Magic.
On the other hand, the facilities on the Fantasy (and I would assume the Dream) were definitely better than the Magic. We travelled with our toddler, and he loved the Nemo splash pad which was much better than the splash pad on the Magic, so that was a big plus for us. The Small World nursery was also quite a bit bigger with more toys for him to play with. Those seem like small things, but for our family they made a huge difference.
So as a previous poster said, there is definitely no wrong answer to this question. We loved both ships. Just think about what is important to you on the vacation.