Where's the best place in the San Francisco Bay Area for a single, 30 year old to move?

I'm going to be moving for a job in Fremont, CA in September and have no idea where to start looking for a place to live. I'll be heading out there for a weekend to check things out, but would like to have it narrowed down to a few places as that's a lot of ground to cover! I imagine San Fransisco is the most expensive and probably further than I'd like to commute, but any suggestions would be greatly appreciated. Would I be better off in Oakland? San Jose? Or another, smaller city? The closer to the coast the better and I'd like to keep the commute within reason. Since I won't really know anyone, it would be nice to be in a young area with plenty to do. Thanks!