(1) First, I tend to agree with russell that Hayward is one of the two most likely candidates for a devastating quake. This fault line seems the greatest threat to the SF Bay Area. That said, whether San Andreas, Hayward or otherwise, any quake on a Bay Area fault line around an M8 or larger will wreak havoc on the Bay, especially along the Marina Green and other places with similar landfill. And I agree such an event is inevitable within the next few years. Fortunately, the seismic retrofits to the Golden Gate and the current rush to rebuild the Doyle Drive Freeway should mean those structures will withstand most anything, as will the tallest skyscrapers around the Bay.
(2) That said, I think the LA basin stands the greatest risk of failure during a quake: from what I understand, LA functions like a bowl of Jell-o, geographically: bounded by the ocean to the west and mountains to the north and east, earthquake waves tend to reverberate within the "bowl" and generate far more damage than they would elsewhere due to the formation of standing waves.
(3) Either way, I think those of us living in earthquake-prone areas need to realize that it is all but a mathematical certainty that we will be struck by another devastating quake within our lifetimes. Accordingly, I think it is foolish to not take at least elementary precautions: I for one, even I could afford it, will simply never live in the Marina Green due to the risk of liquefaction. Similarly, I would far rather live in a tall skyscraper condo rather than a small home since (a) they are designed to withstand quakes far better than smaller structures and (b) it turns out they function like wind instruments (i.e., closed on one end, open on the other): when high frequency earthquake waves strike a tall building, they resonate at a much lower frequency than in a smaller building. These two factors alone -- along with stricter building codes -- explain why we've never(?) seen a modern skyscraper fail in an earthquake.