I had both, although I didn't have dessert at either, but did have the venue, food, and fireworks.
We used Epcot for our welcome party night, at the Morocco location. My guests all loved feeling the "VIP" factor of being roped into that area, and we all loved being so close to the fireworks. The things I didn't like about Epcot were that there are a lot more rules to go by, since it is in a park, and the Morocco location, although beautiful, had 2 parts to it, so my group was separated (the tables were scattered out, and some hidden from other tables).
We had our dinner reception at Sago Cay during Wishes, on our actually wedding night. I was absolutely in love with this location, and honestly, it was my favourite venue out of anything we had during all of wedding events! Something about being at the GF, and being able to see the castle, while in your dress, is just so romantic and magical.
I have photos from both below, although my Wishes ones aren't professional (my biggest regret)! I'm sure you will have an amazing time at either, but I know if I had to choose between the two in the future, I would pick Wishes over Illuminations!
Morocco Welcome party-
http://www.disboards.com/showthread.php?p=36733580#post36733580
Sago Cay Dinner-
http://www.disboards.com/showthread.php?p=36835254&posted=1#post36835254