Since someone asked, let me repeat something that I posted some time ago:
That it is my belief that the Duo-Art is the best system to play 88-note
rolls on with your own added expression.  You have two separate
continuously variable levers to set the Theme (solo) and Accompaniment
(background) levels.  Plus, you have two little levers tubed in parallel
with the "snakebite" accent holes for bass and treble.

With these you can pop quick accents in the music, even better than
sudden jabs with the foot when foot pumping.  Just how much accent you
get depends of course on how much you've advanced the Theme lever over
the Accompaniment setting.  In addition you have the usual Tempo lever,
plus your foot on the sustain and soft pedals.  You can even switch the
Normal-Soft-Dance mode setting during a piece if you like.

Now, the Welte system gives you two levers with direct control over the
bass and treble, and with quick hand motions you should be able to get
good accents, and this may be simpler than the Duo-Art.  However, a major
advantage of the D-A comes with all those Themodist rolls, which are
88-noters except with the accent (Theme) snakebite holes added.  These
let you just set the two main levers on the Duo-Art and the accents come
automatically.

Just as well, since manipulating all the D-A controls at once reminds you
that this is a Musical Instrument and you have to Practice!  When I was
actively collecting rolls 20 years ago there were enough Themodist rolls
around to make this a major consideration.

Since I've never seen a book whose author claimed that "System A" was the
best, I'd agree that the three systems equal out in their good and bad
points.  So roll availability may be your deciding factor.

Welte was first, and German, and so features rolls by the late
19th-century masters.  I've heard that Ampico has more pop and dance
music than Duo-Art, but I've seen plenty for the Duo-Art.

Find out which type of rolls is being recut these days -- that may be the
final arbiter.  Good hunting

Mike Knudsen