We've been on both the Wishes and the Illuminations cruises and IMO the illuminations cruise is a better Fireworks Cruise. But the Wishes cruise is a better overall experience if you're lucky.
You'll have a very short tour around the area, and then the boat will cruise on over to sit under the bridge of the international gateway to watch the Illuminations show. It's close up and a very cool uncrowded way to get a gerat view of the show, and very good experience to have at least once. Once the fireworks are complete the boat starts up and you go back to the Epcot dock or one of the Epcot hotels, disembark, and thats it.....
The Wishes cruise on the other hand was almost like a water tour of the lagoon. We were shown the bear face in the Wilderness lodge, heard the story of the Contemporary sinking, went over the water bridge, and basically just mussed aorund for a fair while. Then we stopped and the captain told us to 'Watch over that way' we turned just to see the Water Pagent start about 50 feet away from us.....VERY COOL!!!
Once the pagent was over we cruised on over to sit and float in front of MK and wait for Wishes to start.
We had not yet seen Wishes at that time, and it the cruise was great itself.....
A few nights later when we saw Wishes while sitting in front of the Castle I understood that Wishes was a FANTASTIC show and really not something that could even be considered as 'Seen' if watching from a cruise. You've got to be up close seeing and hearing it all to fully appreciate it.
So, bottom line, both great cruises, but if you're looking for a great Fireworks cruise, then Illuminations is really the only cruise.
The Wishes criuse is probably better thought of as a night time boat tour of the the lagoon that just happens to stop at a 'good' location to watch the fireworks, and MAY afford you the chance to see the water pagent up close.
Of course these were only our experiences, and yours may be different....... If you have any questions, just PM me.