I loved living in San Mateo. I've lived all over the Bay Area, and that still rates as my favorite. It's a reasonable drive to both SF and the South Bay (and not painful to get to the ocean in Santa Cruz either), the downtown is walkable, and moderately interesting. There's not lots of options for things, but the options are generally decent.

There is zero reason to live in San Francisco, I don't really understand why people are so hung up on it. Live nearby, but not in. You reap all the benefits of the City, without the negatives. Nobody is shitting on your doorstep in San Mateo...