I think I would lean toward the Magic over the Fantasy (only two we have sailed so far). Here is how I break down the differences:
Fantasy Wins
Size - I know some like the smaller ships, but I prefer the bigger size of the Fantasy, particularly the atrium.
Non-Show dinners - I like that the Fantasy has two non-show restaurants, which I greatly prefer, because I am old school and like to be able to hear my family and the servers during dinner.
Ship upkeep - the Magic was showing her age a bit when we sailed, the Fantasy was not (but that was pre-pandemic).
Adult pools- prefer the Fantasy setup, which seems to have much more room to find a lounge chair.
TV - the navigation system on the Magic was so slow as to being close to unusable. You had to click on the remote and wait close to a minute sometimes for the TV to respond. It wasn't just ours, as our Facebook group reported the same thing. I don't remember this being an issue on the Fantasy.
Magic Wins
Food - Food was better on the Magic. I don't know if
DCL has just improved overall, since the Magic was our most recent sailing, but I was impressed with the quality. The quick service was even better and they have shawarma, which was really good. Its pizza seemed to be good enough, while I remember the Fantasy's pizza being terrible.
Aquadunk - my family disagrees, but I find it more fun than the Aduaduck, which is a bit mild for my taste.
Entertainment - I think Tangled is better than Aladdin, but the biggest improvement is the two non-main shows on the Magic. So much better than the really bad ones on the Fantasy.
Adult clubs - I liked the setup on the Magic a little more. Feels very removed from the kids.
All things considered, I could interchange the two and be just as happy, but if itineraries were equal, I would probably pick the Magic.