We used Arrow Agency and are happy so far. We liked them because
* The couple who runs it seems to have personal knowledge of each helper. It wasn't like looking on a website and seeing that "Maria is 25 and married."
* The couple actually run a weeklong training camp in the Philippines for the helpers before they arrive, so they have a sense of their personalities, etc. For ex, we wanted someone very independent and mature, so they recommended someone who fit our needs.
* They do have a screening process -- if a helper seems no good, they won't sign them.
* The agency fees (both the ones they charged us and the one they charge the helper) seemed fair. We didn't want to use an agency that exploited helpers on the other end.
* They followed up with us by calling 2 weeks later to see if there are problems. They have a helper return policy.
Of course, this is no guarantee. There may be helpers who still don't fit in after they get to HK, but we were happy with their service.