SF Chinatown referral
The perennial favorite for dim sum in SF Chinatown is Great Eastern. Some people also like Yank Sing, though it's in the Financial district rather than Chinatown, or City View, which is kind of in between the FiDi and Chinatown.
I haven't been to Yank Sing but have been to both Great Eastern and City View. In my opinion Great Eastern is by far the superior restaurant.