Best LPs to Test Turntables

You should focus more on the cartridge and phono pre-amp than the turntable.  The latter two components actually generate the sound that your hear the turntable just spins the record as long as it does so consistently, not necessarily accurately, you will realize more return by evaluating various combinations of phono cartridges and or phono amps since small subtle factors like frequency response and RIAA accuracy can add audible effects regardless of which turntable you choose.  With regards.

Sheffield Labs direct-to-disc: Wagner, Prokofiev Romeo and Juliette, Thelma Houston. Spectacular dynamic range!

Weather Report: I Sing The Body Electric (The Unknown Soldier). Sweet Nighter (Boogie Woogie Waltz).

Stravinsky: The Firebird (Boulez and the NYP). Mahler: Symphony 1 (Ozawa/BSO) - last movement. St.Saens: Symphony 3 (Barenboim/CSO) - last movement!