Where would you suggest I move within the bay area?

Here’s a little bit about me and what I’m looking for:

I’m considering staying in Marin or moving to Berkeley, Oakland, SF, or Santa Cruz, primarily, but open to other good possibilities.
I’m 28, single, and will likely be looking for work soon.
Not sure if I want to try affording to live in SF.
I’d LOVE to live in a big group house of 5–6 people, preferably around my age or so. Age isn’t crucial, though – I’m real comfortable with people much older than me.
I have hesitations about all the places I mentioned above, but not excited about moving out of the area either.

I don’t want you to feel restricted by only sharing what you think I would love best – I’m as interested in your intuitive hunches about all this.

I have given notice and will be moving out of my home in Marin on June 30. I’m really wanting to feel more connected to people where I live next. Thanks for your input!