There are many maids and services out there that may offer the most convenient availability or the cheapest prices, and these are important aspects of what makes the right choice. Yet at the same time, above all else you want someone who is going to do the job correctly the first time, and that involves more than just simple convenience.
In fact, for anyone looking to hire someone to clean their home and look after their child/elderly, making sure that the job is done right should be more important than making sure it is done as cheaply as possible. After all, if money was the biggest or only factor, you could simply do the job yourself.
So what makes good maids? In many cases, an established track record of good work is the best place to start. Any individual or business can make all sorts of promises about how well they can do the job, but the real proof comes in how well they have shown they can do it.
If you are going to pay top dollar for a housemaid, make sure you outline specific instructions for various aspects of the job that you want her to follow. Good maids will allow you to set the guidelines for how the cleaning should be done and conform to those instructions.
Finally, even though it should not necessarily be one of the major deciding factors in choosing the right maid, sometimes you may have to follow what your instinct tells you. Sometimes, you may feel that she is the correct one. Then, go for it :)