Mom's Best Friend has EXCELLENT nannies and a SUPER screening process. I should know, I used to work for them! Kim Winblood is the owner and I've seen her comments on mamasource so I know she's a member and you can contact her. As far as being a nanny working for the company, it was a little chaotic. However, I was only a temp. sitter so I'm not sure how they treat their full-time nannies. But, they have a nanny training class that all full-time nannies are required to attend and the background check they do is an interrogation so you know you're going to get someone with all the qualifications you want with no worries.
Caring Hands is another agency I used to work for and I really like the owner, Brit Maiden. If you use her, just be REALLY specific about what you want. If you want someone young, degreed, energetic, tell her. I worked for her for two years and loved every minute of it. However, as a mom, I've used her service and have not always been satisfied, though once I learned to be specific, things were much better. Let me know if you have any more questions.
R.