We just returned, and if time is an issue at all I would go to Publix. I think there were more tourists in the Kissimmee Walmart than there were in the parks! We waited in line for at least 30 minutes both times we were there. It was unbelievable. Publix's prices are a little bit higher, but they are reasonable. Shopping at Goodings is like shopping at a big convenience store as far as prices go, so if budget is important I wouldn't go there!
I have shopped at the Walmart during less crowded times and while there are still huge crowds, the wait in line wasn't usually more than ten minutes or so. So I guess it matters what time of year you go. (Although one year a British woman who wasn't used to our steering wheels ran over my foot in the parking lot - so be careful and stay as far as possible from moving cars!)