The Dan! yes, the question could use refining though. If the recording is bad, any kind of music. A bad pressing or mastering what ever. If the recording is noisy or compressed or has background noise that makes it hard to play, or listen to. If the recording is a good one,(any type of music, even country or Hair Metal), the stereo has a better time delivering it. A quip comes to mind, "Don't shoot the messenger".
So even the "Dan" as in Steely, can be a test for a system, but at what volume? In what room, and so on.
But to the assumed meaning of the question, I say Piano is the hardest to process for a stereo at any volume or in any room played by even a master!