From the Cnet review,
"Updated July 8, 2011: After this review posted, we were contacted by a couple of readers asking about the "crease." We missed it the first time around, but looking closely we see it now. It appears as a very slightly darker line running vertically along the left side of the screen, and can be seen most clearly in flat fields of color especially during camera movement. On our review sample we don't consider it a big deal, mainly because it ranges from invisible to barely noticeable in most scenes."
This may or may not bother you.
I'm also a bit put off that the XBR at this price range doesn't have 10 point calibration.
"Update August 30, 2011: We've had the chance to test the 3D picture quality of the XBR-HX929 with new glasses, and the short story is that the issues we saw originally are still there, putting a fly in the ointment of the TV's excellent overall performance. The Sony's 3D image also deteriorates rapidly--losing the 3D effect and becoming rife with crosstalk, as well as brighter and discolored--when you tilt your head "
Not sure if 3D is your thing, but something to consider if so.
"The Sony XBR-HX929 is the best-performing LCD-based TV we've tested this year, outdoing edge-lit models by virtue of superior black-level performance and very good color. Those exceedingly deep blacks don't sacrifice any shadow detail, but the local-dimming backlight does result in some blooming and off-angle issues. Overall, however, for picture quality the HX929 stands above all but the very best plasma TVs, at least when viewed from the sweet spot directly in front of the screen. "
Cnet's take on the VT50,
"As you can probably guess by now, the VT50 earned a "10" in this category. Its only flaws are minor crosstalk in 3D and some wonkiness during my calibration, but neither of those can keep it from taking the 2012 TV picture-quality crown -- and serving as my new reference TV. It's clearly Panasonic's best plasma ever, and creates some stiff competition for the OLEDs arriving later this year."
I think the only reason not to get the VT50 is to avoid IR issues with static images.