I think this question is quite subjective and there will be not one correct answer. I would assume the answers would be based on the person's preference or point of view of a 'beautiful country'. And perhaps, it would be the country that the person answering is living in.
So, to give my 'fair' answer (yet still subjective), I will exclude my own country. Thus, for me, the most beautiful country is Japan. Though I haven't gone to Japan, I see it as a country so advanced in technology, yet still manage to preserve most of its cultural heritage. And it seems nature has her place in a rather, technologically advanced country.