I'm a current resident at San Mateo, and the posters above make some great points. My experience is that it depends on what, exactly, your interest in public or community psychiatry is. If you are interested in learning about the delivery of mental health care to the underserved/underinsured population, then a community program such as San Mateo (there are several others on the west coast as well) might be a better fit. The treatment of the severely mentally ill who lack resources involves a great deal of community outreach, home visits, substance use treatments, coordination of care with social workers and community workers, etc, and it is difficult to grow comfortable with this sort of approach without experiencing it.
That said, getting to see these patients -only- in an inpatient center (which is the case at some residencies) limits the scope of your interaction. By and large, in an inpatient setting, you see people in acute crisis, and your focus is purely on stabilization and attempting to establish some sort of connection to outpatient services. A large portion of the 'work' of community psychiatry is done on an outpatient basis, and so it is important that there be a strong outpatient component to any public psychiatry/community psychiatry program.
Hope this is helpful! I'd be happy to try to help further if you have any other questions!