Hi Joan!
Without a doubt, I would pick the International Food and Wine Festival! The festival is awesome and shouldn't be missed. Basically extra food booths are set up around World Showcase Lagoon representing various countries. It gives guests an opportunity to try new things. I usually try to spend two days sampling food at the various booths. The festival makes visiting in the fall my second favorite time of year to visit, after December. I really don't drink (maybe just one beer all day in Epcot), but I do love to eat and I always have a fabulous time!
There are also special programs and experiences at the Food and Wine Festival that generally cost extra. Some are extremely popular and will sell out almost instantly, so be sure to consider them as you plan your trip.
The Epcot International Flower and Garden Festival is nice, but in my opinion, it simply makes the park more beautiful. Disney topiaries are placed throughout Epcot and there are other special treats, such as a butterfly garden. There are also some special events and demonstrations you can attend in the Flower and Garden Festival Center, but it is nothing like the extra things you can do at the Food and Wine Festival!
You can get more information on the Epcot Food and Wine Festival
here. Enjoy planning and write back if you have any more questions!