Samsung is probably the best line, the Vizio are the bargain line. So if you are real picky about color reproduction, ghosting, and the depth of the black then you are going to notice some issues with the Vizio. That being said, most of the components are made by the same people these days. For normal TV viewing (read, not Blu-Ray) you probably won't notice the difference.
One last thing, I have the newest Samsung LED and it's so good that it kind of freaks me out. Like better than any TV you have seen before and so it doesn't look right. I actually lowered the settings to take some of the sharpness out of it because it was just strange.