I have tried the first one you mentioned, Cheung Dai Wai in Tsuen Wan. Well, maybe I was very unlucky, the maids they have are bad, one of them used detergent to wash clothes, and the other one stole money and also cannot ride in a "private car" as she gets car-sick. Very ridiculous !!
I have tried Anson, they have a training school in Wanchai for the Yan Yan. Actually, a flat above Bar and Club. You will have confidence on them when the contract not sign, when the maid report duty, everything change. I have try 2 maids from Anson, one dismissed and the other stolen my belongings and I called police. May be I am not luck enough to have a good maid or may be I am too harsh to them. Daily duty is playing and take care my 2 years old baby girl and cleaning, most of her time spend in day dreaming and watching TV.
Be aware, some agencies says the Yan Yan may more willing to working in Taiwan now as the salary there is $4,XXX per month. I am not sure it is true or not. But there are some Indonesian operated agencies in Hong Kong that will teach the maids a lot of tricks against the employers.
I have tried the agent Action. Perhaps, my maid up to now is quite good, so I don't think that this is a bad agent.
Of course, the good agent is requried, but it also depends on 個工人本身既性格 & 你既彩數!