The paper roll player piano IS a regular acoustic piano, with a early 20th century design "player" added. This player uses paper which has holes and slots punched into it. Each note is at a different position on the width of the paper. A motor pulls the paper through a mechanism that uses either air pressure or vaccuum (depending on make) to actuate a mechanical device which moves the piano action, simulating a person striking the keys.
The digital player also uses an acoustic piano, however the "player" mechanism is a more recent electronic design that uses recorded digital signals to indicate which note is played and how long it is held. Electrical solenoids are used to move the piano action, simulating a person striking the keys.
In individual cases, it would be possible for either to have the better sound - because the sound is primarily determined by the quality of the acoustic piano to which the mechanism is attached.
In terms of which would provide a greater value and more usefulness today, the paper rolls are somewhat subject to tearing and deterioration due to age; however, they have been made for many years, and some of the performances on them will never be transferred to digital systems. One advantage is that they are generally standardized (meaning that a roll can be played on any player piano - not restricted to certain brands).
The electronic digital players would have the advantage that their media would be easier to make archival copies (there is no evidence that floppy disks or CDs have a longer archive life than the older paper), presuming that the manufacturer did not protect them. There are a number of different systems, such as the Piano Disc player, and the Yamaha DiskClavier. I am not sure, but do not believe that all types take interchangable media.
Also, some systems, such as the Yamaha permit recording as well as being used for playback.
There is also a third alternative - most current digital pianos in the upper ranges and most current synthesizers have MIDI capability with sequencers built in so that MIDI computer files can be generated for both recording and playback.
HTH,
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Jim Cason
Promised LAN Computing, Inc.
Howard C171 Grand, Kurzweil PC3X, PC3, PC361, PC2X, PC2.
JBL 10&15 EONG2s, EV SxA100+s QSC K10s, HP & ThinkPad DAWs, eMu 1820M & 1616M.
Epi Les Paul & LP 5str Bass, Trace amp-cabinets.
Formerly in electronic keyboard repair trade - semi-retired