Vizio has become one of the largest sellers of LCD TVs in the last few years, by putting low prices on good-looking sets. You might want to check out the AVS forums (link below) for the specific models you have in mind.

It's not uncommon for even larger manufacturers to farm out the production of models at one end of the range or the other, or for LCD panel suppliers to vary based on the size of the screen and so on. Couple that with the fact that two or three panel manufacturers fabricate most of the LCD panels used, and differences between brands are not as apparent as they once were.

Here is a link that might be useful: AVS forums

FWIW, Consumer's Reports tagged the Vizio as the least reliable panel tv available.

When looking for a TV last year I looked at the Vizio. I wanted to like it. I tried to like it. I tried tweaking it to make it look better. But no matter how hard I tried, I couldn't make the picture look acceptable. It was always darker and looked like it was a soft focus -- not completely blurry, but not as sharp as I'd come to expect from an HD set. Ultimately I walked away from it and bought a Philips, which had the best bang for the buck and picture quality for the buck I could find. I haven't regretted it since.