Define 'corrupt.'
Do Somalians tell everyone about how they're the greatest country in the world? How their system is perfect and yay freedom and LOVE IT OR GET OUT.
Are violent warlords corrupt, or just...violent warlords?
I'd say we certainly lead in 'advertised cleanliness versus actual corruption' over most. I.e. our government is fucking corrupt, but most people don't know, don't care, or choose to ignore it. Same with the corporations that people grovel at the feet of. 'Thanks for your shitty products and shitty jobs! Yay!'
It's hard to even compare us to something like North Korea, where, yeah, the people in the country are a hell of a lot more misled; but those outside aren't exactly fooled. In comparison, the US is still seen as the 'land of the free' to many outside of it (even if they believe that we oppress other parts of the world).
Basically, 'most corrupt' is just stupid, silly statement that would need a goddamned book to even begin to properly explain the intricacies of.