If you're shopping for a 2012 TV and picture quality is your highest priority, you should, in ascending order of financial recklessness, get a plasma, splurge for an Elite or wait and buy an OLED. If getting the best picture for your money is your highest priority, you should get the Panasonic TC-PST50 plasma -- although the Samsung PNE6500 is a very close second-place. At press time both cost hundreds less than the Panasonic TC-PGT50 reviewed here, and offer picture quality that's just as good.
That's not to say the GT50 isn't worth recommending; it's just a tweener whose reputation suffers the tarnish of comparison--both at the hands of better values like those two, and better performers like its bully of a big brother, the VT50. I love baby G's styling; its feature set is all I could ask for, and its picture quality is among the best of any TV I've tested. Its one seeming advantage over the ST50, a THX mode that promises picture quality similar to a professional calibration, just isn't good enough to be worth the extra money. If you have other priorities, however, such as premium design in screen sizes beyond those of the VT50 series, the GT50 still has plenty of appeal.
Panasonic's content selection is top-notch since it added Vudu, although I'd like to see a dedicated 3D app like LG and Samsung offer.
I mentioned calibration because that's how I compare all TVs--only after adjusting their picture settings to the best of my ability (and since I publish my settings, readers can get their own TVs very close to what I see and compare in the review). But you might be wondering whether the GT50 can beat the ST50 before both are properly calibrated, since the GT50 has the THX modes and the ST50 does not. Comparing the GT50's best THX mode to the ST50's best mode, Cinema, I found that THX Cinema was slightly superior in grayscale and gamma, but dimmer and thus less punchy overall. Of course you can increase the liht output of THX Cinema on the 55-inch GT50, eliminating that difference, but even after that THX on the GT50 isn't that much better than Cinema on the ST50--certainly not worth the price difference alone.