The entire anglo-sphere definitely, South Korea is a good contender... Every country that collaborated with the nazis extensively in the past doesn't really have a good track record even nowadays. France is very, very high up there. But still, these countries do not really compare to the US in terms of being absolutely horrible.
"Oh boy! Can't wait to know all the man-made horrors, war crimes, and crimes against humanity the United States of America did! Just so I can find my hatred of capitalism all the more justified!"
I know, it's just that having the knowledge that they're doing them doesn't stop them from doing atrocities against mankind either. Knowledge is both a blessing and a curse.
We didn't nuke Japan for fun. We warned civilians by dropping pamphlets. They had just weaponized the bubonic plague on china. When the bombs were dropped, they had planned on doing the same biological attack on San Francisco in two weeks.
The Japanese were arguably worse than the Nazis, but their evils during the war were erased because they were such a convenient trading partner. Not even their own citizens learn about their atrocities, especially in the way that Germany does.