The answer to your question depends on a number of factors, not the least of which is how much money you wish to put down. The more you put down, the easier it will be to generate cashflow - in general. So even in San Francisco cashflow can be had. Additionally, the kind of property you want to own as an investment, e.g. single family homes, multi-units, apartment buildings, etc. will make a difference as well. Rental prices throughout the city are currently high and they are still going up.
I can only direct you to neighborhoods after getting some more answers. Feel free to call me at 415-200-7202 to discuss this further.