I used rent-a-mum when I first moved to HK about 5.5 years ago - I believe it is still owned and run by the same woman. She was excellent, and the babysitters she arranged were lovely, usually had some early childhood learning background and were real "baby/kids" people.
The service is expensive, but depends on how you plan to use it. I know she can organise nannies, and a few years ago the salary was about $25K a month. I just used the babysitting service.
When we first got here and I was planning to work I had a 7 month old. I didn't have, nor felt very confident about the domestic helpers and so brought up a nanny from our home country. It didn't work out. The poor girl was very homesick and young.
Our helper joined us soon afterwards - she had a large family of her own and heaps more experience with babies. She's fantastic and is still with us.