Maybe I am just wacked, but I found Fantasmic BORING! With all the hype, I was so excited to finally go to that last year and we ended up leaving. We were like, "this is IT?".
I do find Illuminations magical though, so that would be my pick!
Oh and a pro and con IMO. Fantasmic has a HUGE amount of people packed into a small space and they ALL leave at the SAME time! Down a pretty small walkway too I might add. And if you have to fetch a stroller, WOW! Illuminations is just more spread out. Once outside the gates of course, it is all the same I guess...except Epcot has the monorail system, so many people are leaving on that instead of everyone leaving by car or bus.