The criterion for inclusion was "preserving the Republic and expanding its territory.", so it's hard to say. You could make the case that James Monroe is worthier than either.
Neither. Mt Rushmore is an unbelievably tacky monument (yanks are free to sneer at any comparative British landmark as revenge)
Eh, if they'd followed the original design (complete with the Louisiana Purchase plaque), it would have been good. Or, so bold that "tacky" becomes too small a word, like those never-attempted Nazi and Soviet architectural projects.