I've been back and forth on similar cruises for August and ultimately decided on the Magic.
Why?
1 - In my case the Magic is 5-nights and the Wish is 4-nights. Longer always wins for me.
2 - Lookout on the Magic. Yes, the 5th night means I'm subjected to Nassau, but that's a ship day for me anyway, so no biggie.
3 - I understand that mechanical/plumbing/sewage things can happen on ANY ship no matter how old or new. The age of a ship doesn't really factor into my plan. (well, other than my number 7 reason)
4 - I love that the adult bars are in ONE area on the Magic. Not spread all over and open to any family walking by like on the Wish.
5 - I'm a fan of the atriums on the Magic Class and Dream Class. Not a fan of them being shut off with a stage on the Triton Class.
6 - I will actually go to all the evening production shows on the Magic. I don't like either Aladdin or The Little Mermaid, so I'd be skipping 2 of the 3 shows on the Wish.
7 - While no announcements have been made - and there are older ships sailing - it is more likely than not that the Magic and Wonder's days are numbered. I'd rather enjoy them before my choice is designed-by-someone-who'd-never-been-on-a-cruise Triton class or change cruise lines.