What is they best album out there for showing off the sound quality of your system.

Van Morrison's voice is a tuff test for todays bright speakers.
"The healing game"

Lots of fine recorded songs. Nice bass and background singing.

Black Sabbath (S/T). Loud, louder, loudest !!!

Lonnie Mack-Strike Like Lightning. 
"Oreo Cookie Blues" with Lonnie and Stevie Ray. Some pickin' going on there. 

Doug MacLeod There's a Time

The Harmonia Mundi France recordings of Gregorio Paniagua and his Atrium Musicae de Madrid.  Anything on Todd Garfinkle's M.A. Recordings label.  Yeah, even the CD's have gangbuster fidelity.

After decades in this hobby, my experience has been that people respond most favorably listening to music they like, even more so if I have an album they like that also is well-recorded. 
I rate all my albums on sound quality, classes A, B, C and D. Categorically, the percentages are roughly: 10% class A, 50% class B, 35% class C and 5% class D.
So...I will play a class A or B-rated album in the genre that the guest prefers. Really rewarding to see their reaction for hearing recorded music better than they've ever heard it before. Priceless.