The tracks I most use to tell apart good headphones from the not-so-good:

• Night Club Junkie by YUC'e. The percussion notes starting at 1:14 cover the entire treble range at once and reveal instantly if there are any detail-killing peaks or holes. Makes a nice, crisp, even TSK! sound on well-calibrated speakers and top-end gear, but the consonants increasingly become underemphasized (TsK!) or outright disappear (TK! or K!) as you go down in sound quality.

• Kiseki Musubi by Hololive. The passage at 2:53 features fast tempo, a buttload of instruments covering the entire audible range from 200 Hz up, and vocals to potentially mask it all. Notes are crisp and clearly separated/audible on the upper end of mid-fi, while they're squished together, blend into each other, are drowned out by the vocals, and/or sound like mush on anything below.