[Enthalpy]

Despite jazz pianists use to amplify their instrument, which would enable upright pianos, they prefer grand pianos. Not only for the faster keys.

Jazz pianists almost unanimously prefer Bösendorfer, while classical pianists split among Steinway, Kawai, also Fazioli and rarely Bösendorfer. I ignore their reasons. To my ears, Bösendorfer keeps a clear elocution in very complicated music, while Steinway and co mix up the notes.

 

[Enthalpy]

To make the comparison more complicated: (very) few upright pianos got the more refined mechanics of grand pianos. And giraffe pianos were build, upright but with long strings.