I think El Salvador is the best Bitcoin adoption country right now. They have a small population but already have a policy to apply legal payments with Bitcoin. In the long run, people will choose Bitcoin as a regular means of payment. This will increase Bitcoin adoption rate.
Although the US has many ATMs, Bitcoin is still not considered a legal means of payment like the dollar and Bitcoin users still make up a small percentage of the entire population.
Yes. US may have the bigger population when it comes to crypto users but never has the government adopt bitcoin as a legal tender and still majority are the dollar earners and users. For me, El Salvador even takes the lead in global bitcoin adoption. Although this nation has a lesser population compared to US but its own president has the first initiative to propose a bill making bitcoin as a legal tender. And now, when other countries saw that it was a success even though there were some circumstances that had took place on its first months, start to see bitcoin too which has potentials to be a good currency that will bring progress to the country's economy.