Samsung does handle motion slightly better, people who like LED like Samsung colors better, BUT they buzz. They say that all plasmas buzz, so what's important is considering at what distance can you hear it buzz- you, everyone's hearing is different. Samsungs buzz loud enough for most people to hear it at a greater distance than Panasonic. I can only hear buzz on my 60GT50 if my ear is about 2" from the panel.
If you decide to go Panasonic, then I recommend the GT over the ST especially if you don't have a light controlled environment and want several excellent options for viewing such as Day and Night. It is also a better TV out of the box, but if you plan to have your TV professionally calibrated you can achieve one mode that will match the GT50. In addition, the GT (and VT) has a dual core processor which will allow for future updates that the ST will not be capable of. From what I understand Panasonic may push updates to the GT50 and VT50 will improve picture quality even more bringing it even closer to the 2013 models, the ST won't be capable of doing that processing (no dual core processor).
IMO, the VT50 is not significantly better than the GT50, especially if you don't plan to have it professionally calibrated.
I highly recommend Amazon for an online purchase above all others with the exception being Value Electronics and Cleveland Plasma. However, I believe that Amazon is the best because of their price matching, and return policies.