I would have to kind of disagree with the majority here on parking in SF. I almost always rent a car when I'm in SF. I find that public transportation is very good for the central areas, it is a bit lacking if you want to go out to say Baker Beach. Parking is very expensive at the hotels. But its not usually that difficult to find on street parking outside of downtown and Union Square areas. Even Castro area parking isn't impossible. That being said, if you're on a budget, I would not recommend renting a car.