The original is on Mody Rd. in TST. Classic northern cuisine. Peking duck is ok, but the real draws are the spiced chicken that just falls off the bone, and the meat buns. Really good food, decent prices.
Spring Deer quite famous locally for it's duck, although I prefer the duck in Hon Kong restaurant on Observatory Road. But Spring Deer has a good menu and is always full which kinda shows just how popular it is!
The place is near impossible to get in, I just managed to get a reservation due to a cancellation, it genuinely is the best "Chinese" restaurant in Hong Kong, it is now, officially, my favorite, seriously, it's that good.