as someone working at a kitchen dealer, i can help you here.
Corian is correctly more expensive than granite, and can be moulded around curves, and the joints are seamless, you can also have in built sinks, but in my opinion its too 'perfect looking' and commercial.
Granite is slightly cheaper and is colder, which makes it good for pastry making. I would say granite is more durable too. Both of them will resist heat and staining, and if chipped and scratched, they can be polished out.
It just depends on the type of look your after really.