I agree that all of these are variable. IME, the "shaded dogs" in particular very widely, I have had more disappointments with them than any of the others you mention. I have rarely been disappointed by a Mercury, as long as you stay away from the Wing ones. In addition to the 6-eyes, the Columbia 2-eyes also sound quite good. There are some good labelography sites online, do a Google search and they should come up. There is a great London/Decca one for sure, and a good Mercury one as well.
CLassical: Rca, London, Col, Mercury.....
Rca "shaded dog" LCS-Living stereo releases are highly coveted buy what about the mono(LM) shaded dogs? Are they desireable as well?l Also, what is the difference between blue label and red label London-Deccca releases? Most prefer the blue. In the same train of thought, why are Columbia 6 eye releases so coveted as well? Are the Mercury Living Presence series all that and a bag of chips?