The two cheeses that melt the best are Mozzarella cheese and Gruyere cheese.
Mozzarella cheese has a high moisture content that creates a nice gooey and stringy texture when melting which is ideal for toast, pizza and even Lasagna as well as Nachos or even melting on macaroni.
Gruyere's fat and moisture content help to produce a smooth and creamy melt with a rich and nutty flavor that makes it a perfect cheese for fondue and gratins.
The best cheese to melt on toast is Cheddar cheese.
I prefer cheddar cheese when melting it on my toast as it has a good flavor and melts really good as well.
Other good cheeses to melt on your toast are Fontina cheese, Havarti cheese, Gruyere cheese and Monterey Jack cheese.
If you want a milder tasting cheese that also melts great you can use American cheese or even young Gouda cheese.
If you want a more bolder and more complex flavor of cheese on your toast along with a great melt, then using a combination of sharp cheddar cheese as well as a nutty and savory Alpine cheese like Comte cheese or Gruyere cheese are great choices of cheese to melt on toast.
Medium sharp cheddar cheese is also great and brings a richer flavor for melting on toast.
Young soft or semi soft cheeses like Swiss cheese, Havarti cheese or Gruyere cheese are great for melting on toast and have a high moisture content that means they are especially adept at turning molten.
Even Pepper Jack cheese is great for melting on toast and gives the toast a spicier twist.