If you intend to make a cheese sauce please remember to base it with a rue. Cheese sauce with no rue is quite pitiful and painfully chunky.
Cheese (what ever strikes your fancy)
Melt the butter down and slowly incorporate flour, stirring constantly. For a cheese sauce you want a honey colored rue. Add flour until you get a sticky paste at the bottom of your pot. When you rue is achieved please add, SLOWLY your cream/milk in small increments. Whisk all the while. Slowly add your dairy until you see what looks like a cream sauce and then, over LOW heat, start adding your cheese. Whisk in in 1/4 cup portions, your cheese of choice. I commonly combine variations of both Swiss, German, English and American cheeses.
The whisking is the key. Over low heat. Think of it like a cheesy dream. Create your heart out. Or get medication to control the level of cholesterol that this cheese sauce may bring.