Hey, Angie! My favorite place to check to see which parks I should go to on which days is
www.touringplans.com . If you are not a member of the site, you can click on the link on the left for Crowd Calendar, and it gives you an idea of which parks might be best on which days in the month ahead.
Because it's time for the Food and Wine festival at EPCOT, I would avoid there on Saturday. It's a big draw for the Orlando area locals, and Saturdays, the lines tend to be longer both for the rides and for the food. Magic Kingdom is usually pretty busy on the Saturday of a holiday weekend, so I would say Animal Kingdom might be your best bet.
While you're there, you might want to try out the Picnic in the Park! My family and I love doing this when we are at Animal Kingdom! It's a great lunch break, with plenty of good food, and a bag to cart home all the extra souvenirs in!
Have a wonderful vacation!