The Cambridge Oriental Studies course is better in my opinion - it gives you a whole year in your country of choice, rather than Oxford's measley term.
As for competitiveness, I can only really speak for Japanese (and then only tentatively...) But at the Open Day I was told that there have been years when they've admitted about half a dozen less than the actual maximum for the course, due to a dearth of suitable applicants. In other words, you're not competing against 5 other students like you might be in Economics, you're competing against a set standard, which if reached should guarantee you a place. However, what with the growing popularity of Chinese, I imagine that it would be slightly more competitive.
What is your interest in China btw? Are you aiming for a business career, or are you more interested in the literary side? If you don't mind me asking that is.