I would most certainly without a doubt choose Illuminations!
Great music, fountains, and fireworks with the most spectacular setting in WDW. We always have dinner at the Rose & Crown our 1st night and when Illuminations start I get chills.
James has a good idea...however I think you would have to RUN like H*LL from the Fantasmic show all the way to EPCOT.
There is no way you could take the boat which will wait to fill to the brim at that time of night, stop 1st at Swan/Dolphin, then Yacht/Beach, then Boardwalk, then putt over to EPCOT.
If you did that you would have to ask people getting on the boat at EPCOT, "how was Illuminations?"
Just my thoughts however,
Good Luck!