I'd recommend letting us know what your price range is for a home purchase. There are MANY MANY towns in Marin that are extremely family friendly. The majority of our schools throughout Marin County are top notch (there are a few exceptions). Our county isn't all that big, and every town has parks, recreation, community involvement and more.
There are so many great places and if price is no object, then you can't go wrong with all of our communities. I personally can't pick one that is the "best". I tell folks that ask the same question that usually wherever you rent (if you rent first before purchasing a home) you'll typically end up in the same town as you start meeting friends, get involved with the schools and make it your home.
If you are limited by home purchase price then it's good to limit your looking in those areas that are more "affordable" and also family friendly. It REALLY does. depends upon your home purchase price.
if you are local, or are going to be in Marin coming up, you may want to attend my free Marin seminar that goes over EXACTLY what you are asking. I give an in-depth look at all the towns in Marin, talk about schools, weather, commute times, and more. Here is the link, there are 2 upcoming dates in May and June: http://www.MyMarinHouse.com
I'd also be more than happy to talk to you on the phone if you are not local and gear a "mini-seminar" around your specifics.
All my best,
(and mom 2 young children)
Real Estate Broker and Partner, McGuire