An individual can use bitcoin pretty much regardless of what country. For instance, some freelancers in North Korea even have the ability to earn in bitcoin. Now to the degree as to how much adoption one country has relative to another, I would suspect North Korea to be near the bottom of that list. As would countries with low levels of internet availability and usage.

But even the poorer countries may have higher levels of adoption, due to bitcoin being used because of necessity. In the Philippines, for instance, there's a lot of remittance business done with bitcoin. In other countries with a similar GDP per capital the traction bitcoin has seen is generally much lower.