For me at present for a fancy Thai meal it's: Gang masamam (probably more of a Malay curry than Thai), Yum ped (cold duck salad), Yum neua (cold beef salad), a good fish simmering in stock at your table, Boo nim (fried soft shell crab), and a plate of various steamed vegetables sauteed in oyster sauce.
For everyday: any kind of noodle wet or dry with shrimp, pork or duck, kowpad gung or kowpad moo gaup. Sometimes any kind of good curry, including gang Penang which again is probably not even Thai but damn good even if it blows your head off.
Unfortunately just like in the west, a person tends to latch on to a small list of favourites and stick with it forever. I am guilty of that and am presently making an effort to expand my culinary adventures here. I used to hate sum tum but recently had a shop concoct some using shrimp and mango and I loved it

