I know I'm not answering the question because I find it too lop-sided. Both nations have given.
The Yin and Yang I enjoy about the two nations is the alliances they keep, the friendship, international trade and financing, while still being independent and even critical of the others' ways in some areas.
Yet the two cousins - two huge nations - have survived many years of friendship which I find heartening and which sets an example two nations can maintain individuality, criticism of the other, and still remain partners in what counts - our being joined at the hip, grumbling constantly about the other nation, and still guaranteeing protection and guardianship just as two friends would do.
As much griping about the two being done, I don't often see many other large internationally significant nations locked by land and in cooperation as these two.
Will miss the Olympic Games this year - still relive those last seconds in the hockey finals - beautiful moment for me to see.