When I listen to piano comparisons on line, knowing they are mp3's, compressed file.
I listen for layers that are velocity switched.
Better piano samples switch smoothly and do not jump out screaming of a velocity switch.
Secondly, I listen for tonal quality, to the extent , not too synth.
Playability, and how the samples respond to the touch, are most important...and the only way to judge a piano sound..
Any sample can be eq'd for fullness, clarity, big bottom etc.