First off ... I don't do macaroni & cheese. I make fresh sourdough egg noodles for the occasion. So much tastier than store bought pasta, in my opinion. Cook the pasta in very salty water.
My cheese preference is a sharp white cheddar, asiago and/or parmesan, and white American cheese. Roughly equal amounts of each. I don't consider American cheese to be real cheese but it melts good & helps the other cheeses blend together. Sometimes I make a roux first then melt the cheeses into that. Or else just melt the cheese into some milk & butter (or bacon grease instead of butter). Add salt & pepper to taste. A little nutmeg or paprika gives it a nice extra boost.
The next step is mix the cheese sauce into the pasta. Pour into a cast iron skillet then sprinkle more unmelted cheese on top. Bake in a cast iron skillet until it's all bubbly & delicious.
Now I'm officially hungry.