In Southern California it's best to have a car, especially if you want to see all the sights, which are spread out through San Diego County. There are buses that come to the area, and there's a trolley not far that you can take downtown. (free parking at the Old Town station.) Also from there you can take the Coaster or Amtrak(train) up the coast to Solana Beach and Carlsbad/Oceanside, or even up to Anaheim (Disneyland) and Los Angeles.