More iconic SONG: Billie Jean by a long shot. BJ is probably one of, if not the most recognizable song in the world. Anybody, fan or non-fan, knows it at the moment the beat starts. It's a song that can be played a million times over and never gets old. Thriller as a song doesn't compare to Billie Jean.
Thriller gets a lot of air time during Halloween, but Billie Jean is played constantly on the radio and in public settings (clubs, bars, restaurants, amusement parks, etc) all year around. I honestly think TWYMMF and Smooth Criminal get more radio time than Thriller does. I hear BJ, SC, and TWYMMF the most. Thriller as a song alone just doesn't hold up compared to his other hits.
More iconic VIDEO: Well of course, the Thriller video is more iconic that BJ video. We all know why. haha.
The Billie Jean performance is also very iconic because of the moonwalk, the glove, the jacket and I always identify Michael with this performance more than the Thriller dance. The performance is much more memorable than the BJ video (which is an underrated video btw). Billie Jean is the quintessential Michael Jackson song, and it is his signature song. Overall, Billie Jean is more iconic in my opinion.