I have not done the Illuminations cruise, but have watched the show from the bridge several times. The bridge is not my favorite place to watch from because it seems the wind is often blowing the smoke from the fireworks in that direction. When that happens, the smoke obscures the view.
I have done the Wishes cruise and loved it! The boat captain will stop the boat right in front of the MK lined up with the castle. The view from there is amazing and I have seen detail to the fireworks that I can't see from close up, inside the park.
Have fun!