It is very difficult to define the word best.  Some years ago
I purchased a Steinway K pedal electric Duo-Art upright piano which
sounds very good now that it's rebuilt.  The main factors for buying it
were its exceptional tone which just happens to apply to this piano.

I have heard some Steinway K uprights which are not very good at all.
My criteria would be to find the right sounding upright piano first and
then make sure the reproducing system was working as well as it could,
whether it be Duo-Art, Ampico or Welte.

Malcolm Cole
The Player Piano Group
London