I've never lived in Boston, but I've lived in SF and current live in the Valley and I have to say that SF is awesome for public transit (when it's on time) and SV is better for bike because of the bike lanes. SamTrans on the peninsula is a joke, but the VTA and CalTrain are pretty good. They don't have the extensive coverage of Muni in SF, but if you aren't willing to walk a few blocks to get from a transit stop then you need a car.