Beaches and Cream doesn't have the best cheeseburger anymore. They are serving the same stuff found at the parks. I think The Fountain at the Dolphin has usurped Beaches and Cream for best cheeseburger.
The best cheeseburger I had at the parks probably is the Angus deluxe one at Pecos Bill's. Especially with the toppings bar. The worst had to be ABC Commissary. I would warn people to eat that burger at their own risk. It's really bleh.
As for steak, you will get a ton of different answers. Turf Club, Kona Cafe, Yachtsman Steakhouse, and Le Cellier all have their fans. I can throw Shula's at the Swan into the mix. because they have good steaks, too.