Hi there, Gabrielle!
While all three are excellent options, I would recommend a
Disney Gift Card.
It is accepted at most of the places you'll visit during your stay. And you'll be able to use it on a variety of purchases, from toys to food to paying for your Resort.
There is no fee to purchase a Disney Gift Card. The other two card you mention are not necessarily buyable at a one:one "exchange rate"; some cards do come with fees attached.
Finally, if you lose your Disney Gift Card (and make sure you keep a copy of your gift card number - I like to take a picture of the front and back of my card with my cell phone so I have it available), you're surrounded by Cast Members who are going to do everything possible to help you reclaim it. The same cannot be said for any card that is not directly affiliated with the Walt Disney Company.
Have a wonderful trip!
See you later, celebrator,
-Deborah B.