Miley has much better promotion and her songs have more radio appeal. But Demi obviously has more talent.
As far as who's smarter, business-wise, I think Miley is. We can say all we want about her, but that girl is one of the richest young performers in Hollywood. That has to be because of something.
I think Demi has potential, but I can't shake the fact that she belongs in a pop/rock band like Paramore-ish or something. Her voice isn't good for pop.