Idols, or rather AV stars, as well as some enthusiatic amateurs, in what is technically called “ヘブン状態”, or “Heaven Status”, with the emphasis firmly on their facial expressions.
I leave it as an exercise to you to determine which expressions of orgasmic bliss are genuine, and which merely put on for the camera.
Ecstatic bliss or mere gurning for the camera? Or perhaps you don’t care either way?
I think perhaps 2D is more convincing in many cases; compare against these fine riding videos.