I would do Illuminations and Wishes. I like both of those shows a lot.
I know I am in a small minority, but I find Fantasmic boring. Sure, the water screen was cool for couple minutes, but it dragged on and on. The whole Pocahontas thing is boring (and why celebrate such a flop with as much time as it's given?) I was ready for it to be over 10 minutes before it was over, and then, when Mickey comes out, there was so much mist and smoke, you couldn't even see him, just hear his voice. Lame. After it was all over, we were rewarded with the rudest exit crowd known to man, lost our 6 yr old boy for a panic-stricken 3-4 minutes that seemed like a week, and were basically grouchy for the rest of the night, or at least troubled I would say. Happily, we didn't wait as we went to the second show of the evening - I would definitely recommend that, there were two whole sections (the extreme left and extreme right) empty. If you do it, and they are doing 2 during any night you are there, go to the second show.
The good news for us - we get to enjoy MGM the next time while the masses are waiting in line for Fantasmic. Works for me...