I got this question in my OyeStartups interview.
I answered Switzerland, or Sweden, mainly because the living conditions are optimal for me, but let me elaborate.
South-East Asian countries are cheap, you don't need to cook, and they are full of friendly people - locals and travelers alike - but the living conditions won't cut it. It's incredibly polluted, the humid heat makes me lazy. I don't see myself living there the majority of the year.
On the other hand, my daily life in Switzerland was healthier. Surrounded by mountains and lakes. The fresh air and the clean water. This nature is a luxury. Same in Sweden, full of lakes and forests. Switzerland and Scandinavian countries are expensive because everyone can make a decent living: the apparent costs are reflected in the high-quality of the environment. And nothing like a hot cup of coffee in an empty shop while it's snowing.
Still, the question remains: do I have a favorite country, in general? I gave an answer for the sake of it, but I don't believe in the concept of an El Dorado country. When it comes down to factors I have direct control over - my productivity or my happiness - the environment is not the issue, my habits are.
With the right routine, you can transform your whole perspective of a country, effectively rendering the concept of favorite country meaningless.