The debate continues over who serves the freshest, tastiest, most inventive dim sum in San Francisco: Ton Kiang in the Richmond or Yank Sing downtown. Both serve an astonishing variety of brightly flavored tidbits hot from the kitchen. Both boast lively, attractive, upscale surroundings ideal for every sort of occasion. Both uphold dim sum's immediate-gratification traditions via fragrant steam carts wheeled right to your table. Yank Sing's only real edge, in fact, is the magnificent Ramos Fizz it proffers from its full bar. One might think that this sweet and creamy cocktail wouldn't exactly interact with the pungent pleasures emanating from the kitchen, but one might be wrong. And even if you prefer tea or beer with your dim sum, you won't go wrong with the crunchy-creamy taro balls, the smoky duck with scallions, or the sublime black mushroom-pea shoot dumplings. Another plus: the striking moderne surroundings of Rincon Center, especially the blissfully deco postal annex nearby.