The stall in the MBK food court with the excellent Pad Thai (and terrific fried mussels) is #C15. The stewed "pork limb" at C11 was too bland for our taste.
Two good fish rests. that appear at night on the street in Chinatown are T & K Sea Food, 49-51 Soi Phadung Dao, Yaowaraj Rd. (corner of Thong Suphan No. 453) and Lek-Rat Seafood across the street. We had grilled clams and red fish with "3 flavor sauce" which busted my mouth with flavor and heat. We found these places using the time-tested rule: Local faces and no empty spaces.
For a romantic dinner, "Once Upon A Time", W. of the Bayoke Sky Hotel is pretty; several houses in a garden, but the food was a mixed bag and somewhat expensive by Thai standards (~$15 for two).