I've been on the Fantasy, Magic and Wonder. Of the three my favorite is the Wonder, then the Magic, then the Fantasy. I do love the rainforest room on the fantasy, I actually haven't seen the rain forest room on the Magic/Wonder so can't compare, maybe someone else can weigh in. I don't recall a significant difference in the Oceaneers club. The pre-teen club (Edge) is smaller on the Magic/Wonder but still plenty big. The Teen club (Vibe) has its own pool on the Fantasy, but not on the Magic/Wonder but still its great on both. My boys never ran out of stuff to do and honestly I don't think we really noticed a huge difference. To me it seems the public areas were similar in size between all the ships.
The pool set up seems very similar to me between the ships, except on the Magic/Wonder there are less people so more seats available. The Walt Disney theatre does not have a balcony. They all have a dedicated movie theater and funnel vision. I think you will love the ship. I'm a bit bummed they are building larger ships as I really do like the feel of the Magic/Wonder.