10 being the most comfortable.
Not exactly sure how to define “comfort.”
Probably - Things needed to provide adequately for life to thrive ( peace, safety, sustenance, etc. )
I know that :
1. Most of us are all probably biased ( towards US ).
2. I would imagine that missionary XP ( which is probably the most common long term living outside of the US ) isn’t necessarily indicative of true comfort of a respective country due to the limitations of missionary service.