If they are a great company, just say that you want to work for them because of their good reputation.

If they are a crappy company, they will KNOW they are crap so you will need to come up with a realistic answer. Don't tell them you want to work for them because they are the only ones hiring...that means you will leave as soon as you get a better offer.

Geographic location is probably the safest bet here...you can say that you selected them because you (or your spouse) wants to live in one of their junior domiciles. They have no way of checking on that, and of course it will not matter if you ever actually move there...