Besides the US, I pull for Spain, Chile, and Costa Rica ahead of most other
countries. In general, I pull for teams from the Western Hemisphere over teams from Europe, and countries I've lived in over those I have not.
My three most hated teams since childhood have been, in order, Germany, Italy, and England, although there is a lot of separation between the three. As a kid, I also really disliked Mexico and Argentina, but I later lived in both countries, and my dislike for them dissipated.