I've done every version of redbook
from 'regular old' to 'remastered' to 'remastered from original
source' to 'remastered from original source by Mobile Fidelity';
to XRCD, XRCD2, XRCD24, and K2, sometime remastered
from original source, sometimes not.
IMHO it's 99% about the care taken with the recording, mastering, etc,
not the format named on the jewel case.
I have 'regular old' CDs that rival the latest-greatest K2s,
and SACDs and DVD-As.
But of course we all have to decide for ourselves.
FWIW, another take on it all ...
http://theaudiocritic.com/blog/index.php?blogId=1