I believe that the stereo pressings (The so-called "Living Stereo" pressings) are in more demand and more valuable, although the monaurals I have heard sound great to me as well. Both the mono and the stereo pressings for that era used much better quality and thicker vinyl than the later RCAs (like the infamous Dynagroove pressings, which would bend in a mild breeze). The dyed-in-the-wool shaded dog fanatics seek out pressings from specific stampers, which allegedly sound better than the other pressings of the same title. I have a couple myself, but I have more of the Classic Records reissues, which also sound very good.
Here is something I found online that may be of interest:
What is an RCA "Shaded Dog" record? Why are they so valuable?
RCA's "Shaded Dogs" are their LSC-series (Living Stereo Classical) LPs
from the late 1950s and early 1960s -- the term "shaded dog" refers to
the painting of Little Nipper on the label of these records, which has
a shaded background on a red label. This series was very exactingly
recorded and is in demand primarily among audiophiles who actually
want to listen to these excellent-sounding performances. The mere
presence of a "shaded dog" on the label doesn't automatically make it
valuable; since these are sought out for listening purposes, condition
is extremely important and some pressings (identified by the matrix
number in the runout groove) are in higher demand than others.
This is definitely a specialist's market. If you're interested in
dipping your toes, a book by Jonathan Valin called The Living Stereo
Bible describes the series in more detail.
