it will take a few more months before more extensive in depth reviews become available for the high end models from the 4 big brands, only then will it be possible to make an informed choice
from everything i have read/seen so far, the cadmium based quantum dot technology used in the high end sony panels (HD and UHD in 2013 ) has not been equaled or surpassed for quality in color reproduction. there have however been significant improvement in the brightness levels and contrast, but since almost no video source material (bluray or OTA) uses it, its benefit is mostly on paper as a future potential.
unless you have some great urgency to immediately buy something, take your time to make an informed choice once you have done your background reading and comparisons. the hunt is always more fun then the kill with AV gadgets, and most of us then have to live for many years with the final choice you make
(and with our kdl-w900a's we landed pretty sweetly)