Focus on being Disney fans
I would choose the Magic.
Of the three ships, the Magic has the best stage shows. They have 2 themed MDRs with shows - AP (focus on Animation and has a surprise guest star) and Rapunzels (a birthday celebration with thugs and excellent musicians). It is easier to see the characters as the ship has fewer passengers.
The Dream and Wish both have three stage shows, but I think the Magic's are better.
The Dream has one MDR with a show (I don't think the change in lighting in EG counts as a show). The Crush show can be entertaining, but it depends on how people interact with him. Some think this MDR is very loud.
The Wish has 2 themed MDRs with shows. Frozen is well done, but the size of the MDR means some people cannot easily see. The Marvel MDR is better if you enter Marvel.
If you are in concierge you can request MDR tables and can choose to be closer to the show area.
The Magic and Dream both have nice theatres that play Disney films, including premieres.
The Wish has two tiny theatres that are not really comfortable.
Focus on adults
This is really close between the Magic and Dream.
The Magic has the best adult pool area, you can actually swim! Kids rarely come though the area. Cove Cafe and bars are right there.
The Magic has nice adult areas, but the venues are smaller. They are in an area near each other and there are no kids after 9PM. This is pretty easy to enforce.
The Dream has a pretty good pool area. The deck plan means kids and families are more likely to pass though. Cove Cafe and bars are right there.
The Dream has a nice adult area with more space. They are in area near each other and there are no kids after 9PM. This is pretty easy to enforce.
The Wish adult pool is a joke, as is the adult pool deck. Spread out in a horseshoe shape which makes it hard to access coffee and the pool bars. Very little shade.
The Wish adult venues are in various areas of the ship, so not easy to go from one to another. Some are pretty good with kids after 9, others not so much. This is particularly true of Luna. The cruise staff doing the evening adult shows regularly have to ask kids to leave. As Luna is centrally located and open on 2 decks, this is difficult.
Magic has one adult restaurant, Dream and Wish have two. But, on a 3-night cruise you will miss the MDRs if you go to Palo or Remy/Enchante. On a first
DCL cruise, I might recommend experiencing the MDRs
If visiting CC, the adult areas are separate from the family beaches. Magic will be less crowded than Dream and Wish.
If visiting LP, the adult areas have little separation from the family beaches. Magic will be less crowded than Dream and Wish.
Concierge
Dream probably gets the nod here, - We have sailed the Wish, but not in concierge. The addition of the new concierge rooms on the Magic did not seem to create an issue. We sailed the Dream before the most recent upgrade, so people can share whether they think the lounge is more crowded now.
If getting a cabana is important to you this with be easier on the Magic.
All three have nice lounges, with the Wish having more amenities. Kids have access at all times, and the lounges can be noisy.
There will be special character meets in the lounge.
How much time do you plan to spend in the lounge itself?
So, to sum up, Magic with the Dream a close second.