Gordon Chang predicts China's coming collapse.
I think "collapse" probably overstates the case, but starting during the next ten years China will certainly struggle beyond most present expectations. The biggest reason, though not sufficiently emphasized by Chang at the above link, is its disastrous one-child policy.
China is now the fastest ageing country on earth, and quickly aging countries don't prosper economically. Just look at Japan, or soon to Europe (Italy, Greece, and Spain in particular), for examples.
Fortunately, the US's demographics are much, much better, though they do leave something to be desired.