Hi Jennifer!!!
You have asked a very good question about two great experiences at Walt Disney World! We absolutely love
Fantasmic at Disney's Hollywood Studios!!
Mickey's Not So Scary Halloween Party is also a very unique and fun experience!!!
First off, Fantasmic is not scary in any way. Some of the music and action during the show can be suspenseful, but I would not say it is scary. Our three and a half year old son has loved it since he was a year old and still talks about it quite often!
It is hard to say which one to pick between because they are very, very different. If you are being cautious on how much money you are spending, Mickey's Not So Scary Halloween Party might not be a good option for you. If you have a little bit of extra money that you can spend I would definitely recommend going to the party. You could also easily do Fantasmic if you are going to be at Walt Disney World an extra day and have the day to use on your Park Hopper pass.
Since the number of tickets sold to each party is limited it is a great experience at the Magic Kingdom. We love getting to trick or treat throughout the Magic Kingdom. There is also a special parade and fireworks show for the Halloween party. It is a definite must do if you can afford it!!
I hope this helps and that you have a magical day!!
Scott