I would recommend the Hop On/Off Trolley as the best way to see all the main highlights around the downtown area. The trolley experience was much more preferred over the bus tours that are available. Our trolley driver, Doc, was very entertaining and informative. The stop at Old Town Park is fantastic for shopping and grabbing lunch. There is a stop at Balboa Park, but be aware of your time since it's a huge park with lots to see and do --- and the sites are pretty spread out so there will be a lot of walking! The Trolley runs every 30 minutes at all the stops so you can stay as little or as long as you want at each of the stops. The only caution is that if the Trolley is already full at a stop, then waiting passengers will not be able to board and will have to wait for the next one to come by. I noticed that one stop was packed with waiting passengers but the Trolley company called in some "reinforcement" to get another trolley to accommodate them! Great experience and would highly recommend this tour company!