Depends. Do I have mushrooms? If so, it's mushrooms and swiss. What drink am I pairing it with - cheddar goes well with some beers, but a smokey provalone goes well with others. How cooked is it? What sides do I have?
(See, it can be complicated. And yes, I really have stood there, with the fridge open, looking at the cheeses, the beers, etc and trying to figure out what kind of burger to make. The kids like theirs plain, or maybe with Kraft slices.)