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 60" ZT60, Monitor Audio: Silver RX6, RX Centre, RX1; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D, Panamax M-5100PM
2ch Sony 32" W650A, Sonus faber Toy Monitor, REL T3, Marantz PM8004, Sony BDP-S1000ES, JVC T-X3 tuner, Apple TV, Peachtree Audio DAC•iT, Panamax MR4300
pc Monitor Audio Radius 90HD, Audioengine D1, FiiO A1
+ Sony 65" XBRX850B, Sony BDP-S5100