I guess it depends. Safety--cost of living? The two places that you absolutely do not want to live are East Oakland (some areas of Oakland can be quite nice and awesome, though) and anywhere in Richmond.
If cost is the thing--then on the average, I think South Bay tends to be the most expensive. North of Berkeley is generally more reasonable. You're limited to Albany and El Cerrito, though, before turning into Richmond.
I like this area, however. I don't like much of the South Bay b/c it's very soulless. The same kind of car-dependent Suburban Sprawl that you see all over the country. With Berkeley, it feels like a small town, but also quite urban, in a strange way. In most areas, I'm in walking distance of just about anything I need, which is rather unique for this size town (which does not feel like a city). Can be both quite and lively. SF is just across the Bay, too.
South Berkeley is more or less Oakland, and does suck a bit, but it is gentrifying. West Berkeley (along the bay, used to be a shithole some decades ago (or so I'm told), but it's a rather cool area these days.
Emeryville (er, Pixar-ville), a sliver of a town sandwiched between berk and Oakland, is basically "apartment living in strip mall parking lots." At least, that's what it looks like to me.