That's a tough one. Clinton was mostly corrupt after leaving office via his charity organization. Obama was a Manchurian Candidate/Marxist, who hated this nation and set out to lay the foundation for its destruction, but he may not have been all that corrupt even though he was instantly worth 40 million dollars upon exiting the White House. Biden was hyper corrupt even before entering the Oval Office, but he is functionally Obama's sock puppet and is essentially non compos mentis.
Of the three of them, I would put Obama as the most evil. Clinton as the most post-presidency corrupt. Biden as the most corrupt while still in office.
