in terms of clout, imo it's Harvard
but M.I.T is the rightful one in terms of being the actual best university in the world
Harvard is all-around best in the world. MIT is only good at one thing, so its reach only holds in a few disciplines. Although they have many programs (for example philosphy, economics, music) MIT is only turning heads within math labs, silicon valley firms, quant-banking, and NASA.
Comparatively, harvard's law, medicine, non-CS stem, business, certain-humanities, and economics programs are the literal best of the best. Meaning Harvard has clout and reach in nearly every discipline and every industry ranging from banking to politics to silicon valley to pharmaceutical firms to anthropology/archaeolgy labs, philospohy, hospitals, etc.
Within the brittish commonwealth Oxford has a similar reach; but outside of the former brittish colonies Harvard is king.