I'm surprised no one has mentioned SJC in this thread yet. Isn't it just as close to SFO as OAK is?

Yes, the distances between SFO and SJC and SFO and OAK are approximately the same. However, SJC is much farther from downtown San Francisco than SFO and OAK, and public transportation from San Francisco to SJC is rather complicated.

And IME parking at SJC is a nightmare compared to OAK or SFO.

Since I'm in Santa Clara County, I'll add my 2 cents about SJC.

Obviously if you are in Santa Clara County, or even Fremont (depending on the time of day--I-880 can be a nightmare), SJC is geographically more convenient.

SJC is the other airport for WN in the area besides OAK. It shares Terminal A with AA. The drawback with Terminal A is that lines for security at times can stretch into the car park area. However, once you're past the security line, the gates for Southwest are right there, with little walking (the AA gates require a bit of a walk).

Terminal C is an older terminal with open air gates to the tarmac for the most part. However, at least for Alaska Airlines, the gates are decentralized so that the security line is relatively short because it doesn't share them with the other airlines in C. BUT, the problem with the Alaska gates is that there are no restrooms or food services once you get through security. So use the lavs and get your food first.

This is no longer true. SJC has expanded the secured area for the AS gates to include Togo's and the restrooms directly next to the emergency exit doors. That said, it is still incredibly crowded during most of the afternoon and a miserable place to wait for a flight.

Thanks for the update on the AS gates.

My experience is that for early morning flights the gate area wasn't as crowded. IME you are right about the late afternoon times being packed.