Someone, it appears, was granted a wish. This is what the wished for:
"Everyone on earth must choose the country they want to be a citizen of. They are then given a random social status in that country."
You naturally get a while to do research. Once you've chosen, you become a full-fledged citizen of that country, no matter what you were before. You might be a janitor, a farmer, a soldier, an untouchable, a vagrant, a CEO, a doctor, a celebrity, a prince, or a president, and everything in between. You get all the perks and detriments of that social class- even your health changes. In effect, you become just as if you had grown up into that life as yourself- though your personality, memory, and identity don't change. Your ethnicity might change, if it's tied to social status.
One last thing: This is a weighted probability; if there are ten peasants in a nation and one lord, you are ten times as likely to become a peasant.
What nation do you choose?
I myself would look carefully at the northern European nations. They have remarkable equality and social programs. I am worried that I might end up as a member of the somewhat segregated and disenfranchised minority communities, but I do not know enough to know if that's a serious issue.