An acoustic piano is produces its own natural sound over a spruce soundboard by hammers made of felt striking steel and or copper strings. The quality of the sound produced is a result of the selected materials used to make each instrument, the design of the instrument and the skill of the various technicians used to assemble, regulate and tune each piano. There are over 10,000 moving parts in each acoustic piano.
New or Used ?? "It is not a matter of new or used, it is matter of quality and value."
There is only one rule for buying any acoustic instrument - buy quality. A good quality piano will last a lifetime and second hand in no way means second rate, you just need to know which models to buy, who to trust and what to look for. A cheap new piano can never be as good as a well maintained good second hand piano.
A digital piano is uses digital sampled sounds to replicate the sound of an acoustic instrument using amplifiers and speakers. A good quality digital piano would have a weighted keyboard to a similar weight of an upright acoustic piano. Digital Pianos are usually on a fixed stand with two or three pedals.
Digital pianos do not need tuning and have the option of headphones. Their sound can also be amplified through external speakers. Many also have MIDI.
The quality of digital pianos vary by their construction, sound and touch.
Keyboards do not usually have weighted keys, use only one or no pedals may need external speakers and amplifiers or produce a lower quality sound to that of a digital piano.