Should I buy the iPhone 5 at the apple store or a Sprint store?

If I go to the apple store and tell them I want to get the iPhone 5, will they activate it with the carrier I want? (Sprint) or can I take it home and do it at home? Idk
Or should I go to a sprint store?
~~~~~~~~And another question
So I've seen online that some iPhones come scratched and damaged. And that there's issues with the device like the screen not working blah blah blah...
If that does happen, will apple replace it with a new one? Do u have to pay for a new one? Is there a fee?