Originally Posted by
tmiw
I'd say you need a rental car in San Diego, actually. Exceptions being if you're going to stay in the downtown area or are only going to locations accessible via the Trolley. Taking the bus, while doable, will eat up a significant amount of your time just like in most any other US city.
I have been to San Diego twice and got by without a rental car.
With any city you can find something that you want to see in the area that you need to get to with a rental car.
If you are visiting a city 95% of your stuff is easily accessible without the need of a rental car. The time you need a car the cost of a cab is cheaper than the cost of paying for a rental car your entire trip + parking costs.