In my experience, there are two types of agencies. One is a headhunter who just collects your resume and sends it to the airline. Once the airline hires you, their job is done. The other actually hires you, pays you, administers your benefits and provides ongoing support. It seems to work much better if you have someone in your corner in the long term.
Most of the guys flying in China have been hired directly by the airlines. Anyone know of someone who is working in China? I wonder what the situation is like over there.