I think it depends on the focus of your startup. My perception is that SF is more media-centric, with lots of designers and media professionals, while South Bay

I think it depends on the focus of your startup. My perception is that SF is more media-centric, with lots of designers and media professionals, while South Bay is more "nerdy" and enterprise-centric, with lots of hardcore hackers. Regarding "where to live": I currently live in Mountain View, but I would move to SF if I could afford (although MV is not that cheap either!). SF is an awesome city.