You really have to see both side by side at a dealer. I can't think of a better answer.
My answer is the VT is better because it's more versatile. The VT has inky blacks, great off angle viewing (more practical in a wider room or a room with viewers at different angles), and great motion and "pop".
However, if you need a "bright" TV, LED/LCD is the way to go -- this is better for a room that's inundated with light, many windows, lots of daytime viewing.
The plasma motion vs. sony XBR motion is another -- have to see it. I prefer plasma.
Technically speaking in terms of black levels, the Sony with its local dimming feature will produce better blacks than the VT30, this has been measured by 3rd party people on the 'net.
This Christmas I purchased two HDTV flat screen TVs. The 55 inch Sony XBRHX929 and a Panasonic 42" ST30 Plasma. I agree with the previous post. The Sony picture is precise, sharp, and it did not require any calibration when setting it up. It is amazing that the Sony at the default settings has an amazing picture. The Panosonic requires input from the user as to calibration, etc. I prefer a system that takes the guess work out of the setup. I am not that video savvy as to calibrate a set and know if it's the best picture. The Sony is more expensive, but the picture and relative ease of setting up the TV is worth it. I have been very fortunate with previous Sony TVs as to the reliability, so the added cost may be offset by having a very reliable set for years.
They are about the same, but different. The thing is that they are very different technology and it depends. The sony will definetly give more pop and more vibrant picture because LEDLCD can output a lot more light. They both come with their own set of pros and cons. I am willing to bet that if you go on the showroom to compare the two, you'll walk away with the Sony because of that. Showroom floor is not the most ideal place.
If you plan to use the TV viewing in a brightly lit room with a lot of windows, I would suggest going for the Sony. The VT30 is a plasma and will give you very accurate colors but overall not as bright as the Sony set. I am a happy owner of the VT30. I would've easily been as happy with the HX929 also. At the time of the purchase, the VT30 was $500 cheaper than the HX929. Either way I don't think you can go wrong with any of them. And yes Local Dimming LEDLCD can produce black levels a bit better than plasmas these days.
There is Absolutely No question that the 55" Sony...920...XBR is light years better than ANY Plasma. Especially relative to motion. You are really Not seeing motion accurately on any Plasma because the picture is so non-detailed/inaccurate relative to input. I cannot believe that anyone cannot see the difference. I am very serious when I say that those who cannot see the difference must not have normal vision!