Corruption has traditionally been difficult to quantify. There is the Corruption Perceptions Index, which uses perception as a (clever but tricky) proxy for actual corruption.

https://www.transparency.org/en/cpi/2023

To tie this into your conversation:

Nigeria would rank 145th, the US would be ranked 24th, and the lowest-ranking EU country, if I'm not mistaken, would be Hungary at 76th.