We can't choose between these two places: one of San Francisco's oldest eateries and one of its newest. It depends on our mood. Is our mouth watering for the world's best crab Louis? Then we wait in line on Polk Street for a seat at Swan's well-worn marble counter. Do we hanker for a view of the bay? Then we wait in line at the Ferry Building for a counter seat or an indoor or outdoor table at Hog Island Oyster Co. Both offer an array of blindingly fresh and briny oysters, opened for you when you order them (at least a couple of the offerings at Hog Island come from the company's beds in Tomales Bay). We also love their different takes on clam chowder: Swan's is cream, clams, potatoes, and not much else, served in a deep, thick china bowl; Hog Island's is a shallow dish full of cream, batons of carrot and potato dice, chunks of bacon, fresh thyme, and a heap of tiny clams in their shells.