Every place has a mix of good and bad places. I can't exactly speak for San Francisco because I've never been there, but there will always be good and bad parts of a city.
I hope you have a lot of cash flow. San Francisco is a very expensive place to live... and on that note, most places in the bay area are very expensive. I do not recommend Oakland.
Let's see, for San Francisco... you would have to average at least 3k a month for a cheap place to live and food cost. That doesn't include other bills and basic living expenses (toiletries, cosmetic, hygiene, ext.).
You're welcome! :D