Arguably, McDonald's makes the best hamburger. The fast-food chain serves burgers made from the finest beef, chicken, fish, etc. While Burger King has more varieties of burgers, McDonald's wins with the total number of sales.
The bigger chains are not unbeatable. If we're talking about a specific type of burger, such as cheeseburgers, locally-owned burger restaurants do a better job than their big-box counterparts.
A few local burger restaurants in our area make the best cheeseburgers. The ones at Five Guys', Fuddruckers', Steak 'N Shake, and Fatburger Burger have won people's vote for the best cheeseburgers.