How come the us is friendly with china,but treats cuba so miserable ?:
The U.S. (so the politicians believe) cannot afford NOT to be friendly to China - a huge emerging market, producers of low-cost consumer products, etc.  So even though the Chinese are just as anti-democratic as the Cubans, even though the Chinese undoubtedly have a more horrific human rights record than Castro's Cuba, even though they meddle and interfere with Bush's interests in Central Asia, we give them a pass because we need China as much as China needs us.

Cuba, on the other hand, has very little to offer economically.  So we can afford to play the bully, to assert our Monroe Doctrine dominance over the hemisphere and freeze out the Cubans in the hopes that Castro (or, more likely, the guy who comes after him) will fall from power and we can go back to making Cuba the pro-U.S. cheap-sugar-and-smokes satellite that it was for decades.