Both have pro and con
Both cruises are relaxing and laid back, departs anywhere from 30-45 minutes before the fireworks, cruise around the surrounding areas, arrive and "park" about 5 minutes before the fireworks.
Wishes:
Great view of Wishes, the castle will be just about the center of attention as the fireworks make the perfect frame. Most boats now have the soundtrack, some complain that without this it looses some of the magic, I have never seen this as an issue. Music/soundtrack or not, the view is fantastic.
IllumiNations:
The view is unparalleled! Just imagine sitting on your couch, at ground level, watching one of the most spectacular fireworks, laser, and musical presentations! The music and soundtrack is played from the torch just about 20 feet away from the boat. The entire presentation is just about directly in front of the boats, and the are no trees or obstructions in your view. The smoke and fall-out (pixie dust from the sky), it's always possible, but I would not let this "possibility" deter me from booking this cruise.
Wishes is much easier to book, since there are more boats available and they are not limited in space parking the boats in the Seven Seas Lagoon. Whereas, there are only 6 spaces available for IllumiNations, Breathless is in one space, and that leaves just 5 pontoons. If I had a choice, I would try to book IllumiNations first, and grab Wishes if not available. If I was ever lucky enough to do both on the same trip, I would recommend you do Wishes first, just because of the difference in distance between the two shows.
If you have any more questions about either cruise, just ask.