Let's say I provide a service that is specific to each country. US, UK, Germany, France, etc..
What would be a better approach here:
domain.com
domain.co.uk
domain.de
or
domain.com
uk.domain.com
de.domain.com
These websites will have blogs for content marketing.
I think there are many tools that helps in this situation to find the specific country detail. You can try with this tool https://whereaminow.co/what-county-am-i-in/
I'd go with the second, personally. I think it's simpler for visitors to share a single domain with each others, and simpler for you to maintain. I might also buy the country-specific domains and have them redirect.