San Francisco, but it's hard to say. I mean, if you say the San Francisco Bay Area, and you say the Boston area, then Boston is probably more liberal. But the actual city of San Francisco only has 800 thousand people in it (a fifth of the actual city area is made up of skyscrapers), then yeah it's liberal. But there are areas in the Bay Area that are not liberal. Millbrae is fairly conservative, as are many of the cities in the East bay. The *really* liberal cities are usually the wealthy ones. Oakland and Berkeley, although both have very poverish and dangerous regions, also have the most wealthy areas in the city.
Millbrae is extremely wealthy.