My choice would be San Francisco. Lovely city and easy to get around. As others have indicated, there is no need for an organised tour. You can do a very cheap easy do it yourself tour. Depending on the time of day you can piece together the following options:
BART (Bay Area Rapid Transit) train from SFO to Powell St - about $6 and 30 minutes
Union Square shopping - Macys, Nordstrom, Bloomingdales, Neiman Marcus, Saks 5th Avenue plus boutiques etc
Historic cable car to Fisherman's Wharf - $5 - perhaps stop at world's crookedest street, Lombard St.
Lunch or dinner at Fisherman's Wharf - try crab chowder served in a sourdough bowl at Boudins.
Check the views to the Golden Gate Bridge. Have a look at the seals at Pier 39, and the tourist shops on the pier.
Catch a historic streetcar back to Market and Powell Sts - cost $2. These are old restored trams from around the world, including one from Melbourne.
You are now back at the BART station. If you did not check out the Union Square shops on the way in, do it now. If you have time, Chinatown is nearby and fascinating. Otherwise a short trip back to SFO by BART. Total cost about $20 per person for fares, plus food, drink and shopping.
A notable feature of SFO International Terminal is the food (at least as of 2007). There are two food courts, which feature branches of selected quality Bay Area restaurants.
While I recommend San Francisco, I agree with others that in LA you should take a short taxi ride to Santa Monica. Check out the beach the pier, and the shops on 3rd St Promenade. Particularly good on a Sunday when markets are operating on 3rd St.
Have fun