From my experience in living in Arlington and Cambridge:
Arlington is a 'family-friendlier' area and depending on where exactly, has generally more space for driveways and street parking. For convenience, maybe consider living closer to Mass Ave and Route 16 (which divides between Arlington and Cambridge).
Cambridge will be more expensive in general - but then you have more choices of 'modern' apartment buildings with covered garages. Do check out the Fresh Pond area - there's a mall, movie theatre, Whole Foods, as well as quick access to I-95 and Storrow Drive. I know Alewife Station can appear iffy to some, but during the winter you have the option of storing the car in the public garage there.
Disclaimer: Traffic can be really bad during peak hours!