I know San Diego very well (my parents live there), and when I hear of someone considering staying downtown I shudder! San Diego has one of the nicest beaches in America, and one of the most boring downtowns in America. With the exception of Balboa Park and convenient access to the Trolley, why would you want to consider this option? First of all, yes, you certainly must have a car here. Traffic can be a problem in this area, and summer tourists love this town too much. You will want to see Tijuana also, but you should take the trolley, since it's fun, and also since you will not have to worry about parking at the border. I realize that rooms near the beach will not be plentiful on PL & HW, but DO NOT STAY DOWNTOWN! Harbor/Shelter Islands are just next door to the airport and downtown, but provide a much nicer atmosphere. Point Lobos and Pacific Beach are also possibilities. The town of Del Mar is fabulous, as is La Jolla (the wealthy). Coronado Island is another very good choice - this has the largest beach. With all of these great options, treat yourself to a few extra pennies, and STAY THE HELL OUT OF DOWNTOWN!