Very difficult, almost impossible to say. When it comes to book smart it is most likely Obama. When it comes to political smarts it possibly is Cheney. When it comes to political wheeling and dealing it will be Cheney too. When it comes to emotional intelligence it will be Obama.
The 2 are not really that comparable, both are smart but mostly not on the same subject/categories. So all in all I cannot say who is smarter, though IMHO I think that Obama would win out in the end, but that is just an opinion. For all I know Cheney would smoke Obama in an IQ test.