I am rather curious about it - free from emotions. Where do you get this conclusion from?
Are you thinking about specific countries? Or how you you get to this superlative? Because of so many cultures living in it?
I didn’t know so many people would focus on that statement

. It wasn’t based on any study or anything I heard an expert say. I am basing it on my experience growing up on different continents, traveling to more than five dozen countries, talking to the local people and friends in other places. Was I discriminated against in any of those countries? No. But you do know which countries have overt racism against which groups. E.g. Almost every country in Asia has an overt racist prejudice and bias against a black (African descendent) person. Asia stretches from Japan to Middle East. Japan discriminates based on gaizen (foreigners) vs nihozen (our people) but it is very covert and matter of attitude. Japanese is most homogenous society as you can find I think. The Israel discriminated against black Jews from Ethiopia and other places. Not to speak of political discrimination against its Palestine population. Many middle eastern countries discriminate against the south Asian work force / immigrants the same way Hispanics and Mexicans get discriminated in USA. UK has its colonial past that shad reflected in discrimination against the Indians, Pakistanis and Bangladeshis who have settled there for generations. A famous quote I heard and like about someone questioning why people from former colonies are “here” (in the country that colonized them). Someone answered we are “here”, because you were “there”. A very apt answer in countries like Britain and France that have multiple generations of ethnicities from their former colony. I guess we don’t have to get into the issues discrimination faced by south Asian descendants in UK, or North African descendent in France it Belgium, or the discrimination in Germany against the Turks. For god sake Europe was almost outright hostile to Turkey joining the EU.
When it comes to conquerors wiping out and continuing to discriminate against the indigenous people, all of the new world the Americas, Australia and New Zealand have very shameful history. Canada, New Zelaland and Australia are still struggling to right the historical wrongs. The South America doesn’t even pretend to try.
So that leaves sub-Saharan African that has no one to discriminate against. Not really. Like in many other countries there is discrimination there too based on religious, regional and tribal affiliation. Remember horrible Hutus vs Tutsi civil war/genocide in Rawanda ? ( the ironic part is the Hutus and Tutsis were artificially created constructs by the British during colonization). The apartheid in South Africa or religious based conflicts in the central and west Africa.
Other than Antarctica which continent is left

.
Till recently and through the 20th century, the USA offered best chances of upward social mobility to immigrants and individual members of disadvantaged communities. It has least restrictive laws in my opinion for the foreigners to proper and succeed. Canada may be a close second.
I think when we look at discrimination and racism we have to look at it from different lenses:
- internal discrimination within the locals themselves
- discrimination against outsiders/foreigners/immigrants
- redressal mechanisms against individual discrimination
- anti-discriminatory laws in the books
- enforcement against discriminatory practices
- systemic and institutional discrimination
- people’s attitude in general against those who are different from themselves.
Taking all of above together I think USA does better or may be it is my bias. I think North Americans as a community and USA as a place is overall more tolerant than other equivalent large communities like Western Europeans, Russians and Eastern Europeans, Indians, Middle East, Chinese, Japanese, SE Asia, and Latin Americas.