Choose a good melting cheese. Muenster is a very good choice, as is any other soft cheese such as Monterey Jack, Pepper Jack or Cheddar. Avoid hard cheeses like Parmesan, or a Mexican crumbling cheese such as Cotija. I also don't like to use Mozzarella. Even though it's a great melting cheese, it's strings once it's melted, making it hard to eat.