Pretty sure this has been discussed on here before but I'll put my two cents in. They're both excellent performers and are two of my favorites. Unless you're staunchly anti-plasma, I think most would agree that the VT50 is the better TV, however. I've seen and tweaked three different 55HX929s, and they look great but suffer from excessive blooming, which is the only real knock I have against 'em. The 65HX929 I saw looked much better with very minimal blooming - I'm assuming because that model has a higher zone count. Being a plasma, you don't have to worry about blooming or backlight irregularities with the VT50. I don't think you can go wrong with either set, though. Personally, I chose a VT50 and don't regret it one bit.
ht Panasonic TC-P60ZT60, Monitor Audio: Silver RX6, RX Centre, Radius 90HD; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D
2ch Marantz PM8004, Sony BDP-S1000ES, JVC T-X3 tuner, Monitor Audio Silver RX1, REL T3, Apple TV, Peachtree Audio DAC•iT
lr Panasonic 50ST60, Sony BDP-S5100