The absolute best steak I've ever had (not just Disney, but anywhere) was at the Yachtsman Steakhouse. It was cooked perfect (I like well done), very juicy, tender, and flavorful. You could cut it with a fork, it was that tender.
I have also had good steaks at the Concourse Steakhouse and Le Cellier, but they couldn't hold a candle to the Yachtsman steak.