IMO, its Trump.
With absolutely no hyperbole, he is literally unqualified to hold most stations of public office, let alone the most prestigious and most visible role in the US government.
He is an act of psychic vandalism against the people of the world, inspiring and emoboldening the worst of the public to be worse versions of themselves. He actively undermines faith in representative democracy, the prestige of public service, the integrity of his station, the accountability of his role, and the civility that keeps a country full of different hearts and minds working together for a common good.
I would have voted for Bush, who is a close second place, but you could argue that much of the evil he brought into the world was actually ushered in by Dick Cheney and his political machine. I also believe Bush feels sorry for what was done under his leadership, something I don't believe Trump is capable of.