Most travelers trips are to fisherman's Quay which expands between Pier 39 and Ghirardelli Square. It has got a lot of souvenir shops, inexpensive hotels, loud attractions and fairly priced "museums". It is an intensely noisy place too. But, it was and it is now a genuine fisherman's wharf.
You will find a few superb places, spectacular views and tons of excitement here. In the past couple of years, some six hundred Californian sea lions have taken up home on the contiguous floating docks. Until they dump their new playing field that looks to be more unlikely, these frolicsome creatures ( some nights you might as well hear them all the way from Washington Sq. ) are one of the greatest free attractions on the quay. Docent-led programs, available at PIER 39 on weekends from 11 am to 5 pm, educate visitors about the variety, environment and malleability of the California sea lion.
Cotton candy and souvenirs are all very well and good, but if you wish to get to the original history of the quay, which is boats, there is no better place to do it than by the pier, definitely one of the quay area's most fantastic attractions. Depending on the time, you might see ship builders at work or family manning a ship as folks did in the early 1900's. Don't stay away from the pride and joy collection of consequential vessels, part of the San Francisco Maritime State Park, all of which may be boarded.
Some folks fall in love with Fisherman's Quay while others cannot get far enough away from it. Most however agree that, for better or for worse, it has got to be seen once or more in your lifetime.