I guess I mildly root for Poland, Germany, and Croatia, the main areas where my ancestors came from, but it's nothing strong or anything. It's more like if I'm watching a sport where it's between say.... Poland and a couple random countries, I'll just say, "Go Poland," but not really care one way or the other beyond that.
When it comes to the Winter Olympics though, I usually root quite well for countries that have Hawks on their hockey teams, until they come across the United States, of course.
China especially since so many people in the U.S. are openly racist or have hatred against Asians. I'm like, 'what the heck, most of us just go to school and try get a good job!'
People dislike the Chinese team because of their long history of cheating, using underage girls in gymnastics, and country's human rights violations, not because of racism. I cheer for Japan consistently on a personal basis and I'm white, so it's not an ethic bias present here.
That and the Chinese are just so damn good in virtually every single discipline. People are always going to hate on the most successful countries, right?