What is your goto reference recording

I’ll echo the assortment or compilation theme.

I enjoy many genres. Consequently I should have a bit of each one that has distinct items I’m looking for a ??? to exhibit or demonstrate. Bottom end performance; midrange; top end finesse; sound staging; area of the sound stage; amongst these tracks I should get some pretty good idea of what to expect. I use Jazz, blues, R&B, folk, country, alternative rock, rock, acid jazz, choral, acoustic and metal. I have a couple tracks of   Acapulco singers, male and female. Baritone Sax. Drums of course.

As said, I can’t see how someone could select ??? using but one sample of any music, unless that was the only music genre they listen to.

Put them onto disc and HDD, or bring along a couple LPs.

I like to use my British EMI pressing of PF's The Wall. Plenty of variety on the two LP set for some fun listening!

+1 mapman

I also use a CD I burned with many familiar but different pieces of music.  I think that Paul Desmond's alto sax on Take Five is a very good indicator of whether a speaker will exhibit objectionable harshness later on, BTW.  Other pieces include male vocals, female vocals, solo piano, and some other esoteric stuff I like like Lambchop.  
Having stuff on 1 CD saves the distraction of getting up and changing CDs or LPs.  

Zappa-Apostrophe